Module V - Cities, Villages and Interiors
Of all the modules in this part of the guide, Module V is beyond a doubt the most complicated one. On the hand, ensuring compatibility with other mods editing the surrounding while maintaining good navmesh paths for the NPCs to walk on is important, on the other hand there are so many different areas they touch, requiring a large amount of patches. Eventually I decided to go with a single set of compatible (and lightweight) mods to overhaul some of the towns and cities.
I will add more options and possibly a guide to mixing and matching the larger overhauls with each other in the future. Open Cities Skyrim might be added as well. Eventually I hope to cover all cities / villages in Skyrim.
Major cities and smaller towns
Because of the many different mods in this category plus the amount of work one can put into mixing and matching them, I decided to - for the time being - stick with my Classic Skyrim favorite to cover the five hold major hold capitals: JK's Cities Lite is in my opinion the optimal choice in terms of both performance and consistency. As a stripped down version of the original JK's Skyrim hold capitals, it blends in well, improving the cities noticeably without making them appear drastically different.
In addition to that there is Arthmoor's suite of town improvements which is modular. They should not be mixed with ETaC - e.g. don't install both Arthmoor's Darkwater Crossing and ETaC's Darkwater Crossing - but there are patches for JK's Skyrim, meaning you can run all of Arthmoor's town mods alongside JK's Skyrim.
A note on Arthmoor's town mods: These are very small and lore-friendly additions, often adding a house or two for strangely homeless villagers. You will most likely not notice you have them install, which is not a bad thing at all. They blend in perfectly. The all-in-one version has not yet been released for SSE yet so all of Arthmoor's mods together take up a total of 11 ESP slots. Whether simply unpacking the BSAs and merging the plugins works out well I have not yet tested.
This section is so far still very small as I basically just recommend Distinct Interiors for everyone. Be warned that Distinct Interiors also overhauls the player homes in each city, adding several different options for each. I do not recommend installing other vanilla player home overhauls with Distinct Interiors unless you did not install the Complete version and went for the Modular one, skipping the Player Homes module.