As Jim said, there's going to be a lot of personal preference involved here, heavily dependent on how you see your world setting developing, what types of civilizations exist in different places there, as well as how much time and effort you have available for designing and mapping it all.

Plus you're really asking two different, if related, questions - 1) the number of key buildings desirable for different types of settlement, and 2) what the appropriate size of different types of settlement can be for different types and numbers of special buildings.

The question of settlement sizes has come up on the Forum here before, and you might like to look over the comments on these two topics, both of which coincidentally came-up in late 2018:

Making a city with CC3+

Looking for advice on starting Village/Town/City size

There are also various systems for designing RPG settlements available online, some paid for (on sites such as DriveThru RPG), some not (such as blogs), as well as a number of random design systems, such as those on the Watabou site, although those provide primarily maps, rather than lists of the specific places you indicated as of interest.

Those should get you started at least, or perhaps help clarify what it is you want (or even don't want!) from such systems, from where you might feel more confident about creating your own settlement design system.

Good luck!

Looking at the symbol and terrain use here, I think these could be used to create an illusory city too, or a literal ghost town, perhaps with some additional colour overlay effects, and perhaps some transparency about the symbols (less sure about the latter point, however). Or indeed a city of glass.

While the size may seem wrong, by a strict comparison with some medieval European structures, this isn't for medieval Europe, it's for fantasy D&D, and is close to the scale size for this specific tavern as shown on Mike Schley's map of Saltmarsh in the Ghosts of Saltmarsh scenario book (Wizards of the Coast, 2019), assuming five-foot grid squares here. The appearance isn't quite the same as on that map, but this is an adaptation after all, and although there are a number of designs for the Wicker Goat Tavern online, I don't think there's an official D&D version, so some leeway is to be expected.

In the original adventure (The Sinister Secret of Saltmarsh, TSR's Module U1, from 1981), you were expected to create your own version of the town from scratch - there are a few guidelines for key points, such as Point 4: "Decide where the characters could stay when resting in the town between adventures (the best inn? the only inn?); draw up a tariff (list of expenditures) for their accommodation and food." But that's as close as we got to a description for the inn/tavern, which didn't even get a name back then!

That's not to say such points should just be ignored necessarily, and the heating and access points are useful considerations. However, if the final tavern is meant to fit to the size of the official Saltmarsh map, this is close enough to work for that.

Might be worth tweaking the glow on the lettering to help it stand out more. Might be the colouring instead, but I'm struggling to pick out the numbers for some of the features on the map, and I get the impression the red doesn't seem so clear on the background as the black.

See this blog article by resident CC3+ expert Remy Monsen. Hopefully, that should help, but if you get stuck, feel free to ask here again!