Read osm.wiki/Tile_usage_policy for a kind-of checklist; from what you write the first part seems covered, but do look at the section Technical Usage Requirements and onwards.

Having all highways with a maxspeed tag set will happen before every house has a addr:housenumber - which is a goal that will take some years even in towns with active mappers. Just get on with it, you'll have your local area covered soon enough even if you collect just one speed limit every day. Make the most out of your mundane travels by introducing slight variations.

A week ago I was the last editor of 6300 objets containing house numbers just in my home town. The number I have entered is roughly the same, in this city. And we only have about half of all numbers yet. Add to that a few hundred on trips to other places. Point being: yes, it's a lot of work.

Especially when there's lots of stuff already drawn, I often don't do full mapping surveys (with a camera, hundreds of photos and days worth of editing), but I'd be reluctant to let the daily trips be a total waste of my time, mapping wise:

If you commute by car or on a bike, you can often choose a bit different route every day. Then you can usually survey one or two blocks / bits between two intersections just by memory; "on this section, there were roughly equally spaced houses, odd numbers only, 8 to 22". Repeat the next day. It is more foolproof if you try one side of the road only on any single trip.

If it's a long section or they're not roughly evenly spaced and you're on a bike or on foot, you can stop for few seconds in front of each one. Just limit your eagerness while doing that, so that you don't have hundreds of stops in the gpx, but already forgot which numbers they represent. If you use a bus daily, and the buses leave with a suitable interval, you can do such sections, too; step out at a random stop and walk to the next stop (or the one after that), again stopping in front of each house. Then you might as well have a bit of paper with you and write down the numbers in order. Extends the area covered for little extra time spent.

Do check if it applies in your country: some countries have made "systematic" depth measurements a licensed activity; they consider the data too interesting for hostile army vessels and want to keep some navigable waters a secret - thus the licensed surveyors need to present their data for "cleanup". But if they can't know who you are...

Someone did experiment with generating terrain data from a pile of gpx logs elevation data. I got the impression that only after tens of traces for each road the values start to converge to a reasonable presentation, i.e. without nonexistent hills or cliffs. And only for that road. Sorry, no link at hand.

Introducing highway=road was even discussed only after the import was already done.

There's no reason not to add detail to railways, too.
osm.org/?lat=60.22&lon=24.944&zoom=16&layers=B000FTF
There's also a page of examples of detailed mapping of several feature classes:
osm.wiki/Sample_areas

The key surface is not even looked at in the rendering rules, AFAIK.

Could be that they've used some preliminary city plans to draw their map and got the wrong name from that. Or it's intentional. I've seen some footways with a name ending in "tie", but they're mostly some really old and narrow roads that have since been barred from motor vehicles.

Again I'd say leave them in. They're of little use in the beginning when all there is are the street shapes and names, but in some years they can be. At least in places with all the buildings and house numbers and with out-of-the-ordinary street shapes, they start to make the highest zoom levels more informative than any simple-to-use tagging scheme could. With them it's easier to enter the pedestrian crossings and their reachability without compromising the accurate connections to some footways in the parks, or such.

If you look at most (state) mapping agency produced map databases, they do have driveways. There's so much more to maps than the "public roads for routing" - yet mapping of which is the first objective. Leave them in, someone will eventually (could be years but anyway) add them again.

Just by looking at the aerials, I don't see a reason why not to draw a footway to connect the barrier=entrance to the road by the church. I'd personally draw all the significant parking areas, too, with an access=private where appropriate.

Just a comparison of the amount of roads... (numbers from wikipedia so I don't know if GB number includes all forest tracks accessible to cars - for Finland it does)
Km of roads, population, land area (km²)

453 000, 05 300 000, 338 419, Finland
398 350, 58 000 000, 209 331, Great Britain

roads/person: 85 meters (FI) vs. 6,9 meters (GB)
roads/sq.km: 1,33 vs. 1,9 km
(actually 1,49 for Finland as 10% of land area is lakes)
roads/local OSM user: 1058 km (FI) vs. ?
sq.km/local OSM user: 790 km² vs. ?
And then just guess how much unmapped roads we have here outside the biggest cities...

The land borders between Finland and Sweden and Finland and Norway run mostly along a river. I was searching for their data from the local officials but found only some information: the borders are checked by both countries authorities every 20 or 10 years to see if the deepest or "main" route of the river has changed considerably. The surveyors jointly produce a list of the control points for each country's higher officials to approve later on. Last time this was done Finland gained a small island but lost some even smaller islets, if I remember correctly.

On the Russian border the same procedure has been carried out sometime but there's no river, only the poles, so it's more straightforward and even considered more seldom.

Combine barriers with suitable access tags and values. For the first one: barrier=bollard + motorcar=private. The open metal bar with motorcar=permissive.

High tide was mentioned somewhere in the wiki as the correct practice and some have discussed how to tag the mean and low tide marks, current best might be
osm.wiki/Tag:natural%3Dwetland

So far adding the traffic_signals is much less important than having the geometry of the crossing ways sufficiently correct. If the signals are just marked on the various crossing nodes, someone can then later use a relation to tell routers about the synchronizations and such about all the traffic signals in one intersection, once someone (else) has proposed an adequate relation osm.wiki/index.php/Relations/Proposed/Traffic_Lights for such use.

Any technical profession and hobby has a gender bias, from devastating to negligible. Be it technical university education, freight transport or car sports, the women are a minority. Of these only car sports attracts female spectators (which could want to try the sports themselves) because the drivers are showing off their sport skills; there's nothing hormone rush inducing in shouting "look at my big map!" (just as "look at me solve this with a 17th order Laurent-series" might appeal only to math professors)...

Also, the male mappers are (for the most part) either outdoor people (hiking etc.) or the geeky type (like me). Most of the active outdoor-hobbyist women are more likely to concentrate on the doing the outdoors part, not on watching and correcting the map. Technically oriented geeky women are such a minority (and only sociologists can try to explain why) that it'd be as probable to find a fairy flying around with a gps.

(I could and should refute the points in the previous comment, except for the first one, but I'll limit myself to the notion that point 7 is definitively solved by photomapping.)

Anyone driving from north to south never touches or crosses the lanes for driving from south to north. There's space in the center of the intersection that is used for driving east-west (and turning), but only because the nondivided road crosses and connects the separated roads. Keep straight roads straight has been in the editing standards as far as the wiki history goes and the recommended practice in all mailing list discussions. If the crossing road didn't exist, there wouldn't be a turn in the separated carriages so there shouldn't be one when the crossing road is added.

And I didn't mean that one should draw each traffic signal pole, but one could. Eventually someone might be adding pedestrian crossings and having the traffic signals drawn as being only after the pedestrian crossing would then seem illogical.

As for the second example I admit that neither is optimal but having both (the non facing) roads drawn straight across the bigger road is IMO closer to reality: driving across the bigger road includes first turning (almost) parallel to the bigger road and only then turning to the other side. At some point when the offset of the non facing roads get smaller it becomes reasonable to connect them directly, i.e. the crossing just south of your example looks like one. A driving direction "drive straight" wouldn't be confusing in that when crossing the bigger road, but the example intersections is more accurately guided as "turn right and immediately left".

1) Do the lanes in the separated directions curve into the intersection? No, everyone drives straight.
2) Do the lanes in the separated directions touch and overlap each other in the intersection? No.
I really urge these should be drawn "as two parallel crossings". Location of the traffic_signals is not yet used for anything and they might as well be added as separate nodes on all incoming ways at the exact point where they are.

You can add a tag 'postal_code' on any street.
The more common/proper/first in the street sign/official name goes in 'name' and the Welsh name in 'name:cy' or the enter the English name as 'name:en' if the Welsh name is the "primary" name. The two letter codes for languages are the same as in some standard. That's how it's done at least in Finland where we have both Finnish (name:fi) and Swedish (name:sv) names for many of the streets. Only what's in 'name' gets rendered, for now at least.