This is all great feedback! I'll respond to Kana's point because its framed as questions and they seem to cover a lot of the things you guys are asking and are nicely organized.
Keep in mind, I'm not saying that I have any of this right yet, but these kind of outline my goals, so maybe you guys can help me make the gameplay match up with them.
Kinggath, what is your frame of reference for what the stages of a settlement growth should be?
I approached it from an expected number of settlers and used food and security as the primary limiting factors of growth. I tried to steer settlement building towards a certain optimal path that would reflect the realistic needs and priorities of these people as if they were survivors trying to settle down.
So rather than civilization milestones, I tried to use population milestones and the types of groups that might form, to determine how things might pan out, and then put the numbers and conditions in place to encourage using certain plot types at different points. The milestones I always used were: Starting Population (1-3 in most settlements) - this represented a farm family just doing what they can, 5 settlers - representing multiple families coming together to establish a settlement, 10 settlers - representing a turning point from struggling survivors to established self-sufficient town, 15 settlers - representing a trading town capable of producing excess, 20 settlers - a full blown Fallout city with all of the amenities and even time for luxury like investigating new technology.
Do you expect it to be without power and defense till a certain number of settlers?
That is how I like to play it. I refrain from powering anything but necessities, which functionally are only the Martial plots. Homes, shops, and basic industrial will function without power. This not only reflects the reality that power should be hard to come by, but it also controls upgrades. I think most people see the power symbol and assume "Needs Power", but for those three plot types (Residential, Commercial, Industrial), I'd say it would make more sense to treat those as "Can Be Powered". Unfortunately, the UI doesn't allow for the distinction. It was something I hoped people would pick up on (the idea of not trying to get everything to upgrade super fast by controlling power), but when I recognized most people were immediately powering everything, I added the Upgrades: Manual option so players could just hit the breaks on those upgrades without having to worry about controlling power. It's still not a perfect solution, because it introduces more micro-management.
Any suggestions on how we could imply this as a good play style? I love to make as many things as possible intuitive, with visual or audio cues, and UI pieces that point you in that direction as opposed to pop-up messages and required video watching or forum reading...
Is it supposed to be balanced towards using vanilla workshop items all the time, just in certain stages, or never?
Yes, the goal was never to fully replace the vanilla objects (or mod/DLC added objects). I tried to discourage the idea of using plots for water and power early by putting them on plots with high penalties. I think using gasoline engines and hand water pumps is actually awesome towards the feel of a growing post-war society.
I've always loved the idea of the settlements being more fluid, where eventually some of those old things become obsolete as you expand your technology and resources. So for example, in the mid game, destroying some of those hand pumps for a Community Well, which will then upgrade and supply most of your city's water. Or tearing down an unneeded farm and opening up a factory in it's stead.
I think turrets are a big problem, and if I wasn't against altering vanilla items, I'd have upped their cost or put a perk requirement on the starting ones. Automated defenses should be a later stage luxury. I actually love turrets, and don't want to replace your need for them fully, especially in the mid to late game, where having your settlers on production would be more important. So reducing defense requirements in the early to mid game actually sounds like a perfect idea to push gameplay in the direction of treating turrets like a luxury instead of a requirement.
Defense is a tough one, because if you artificially inflate the numbers, your actual ability to fight off a raid isn't accurately measured. For example, if the Martial plot gave 15 defense to start - it's still just one guy standing behind a post, whereas 3 turrets (which also provide 15 defense together) are basically the combined equivalent of a dozen settlers with pipe-rifles.
Definitely sounds like defense needs to be bolstered - but perhaps instead of direct bumps to Martial plots, we could do it some other way? For example, reduce the defense penalty on homes by half. Or create some low-tech alternatives to turrets that add to defenses - maybe we need some more non-technological traps in the game?
Does the current balancing assume settlements will support each other in the future, or balanced for each settlement being self sufficient?
The balance was definitely built around self-sufficiency, I spent a lot of time building Sim Settlements and Industrial Revolution in spreadsheets. When I finally get to the point of coding proper shared resources (not the half-baked method Bethesda used of literally "eating and drinking" food and water items from other workbenches...), I'll probably have to re-balance all of the numbers accordingly.
What settlement sizes are expected to be capable of being self sufficient, producing all their food, water, defense, power, and happiness?
Every size settlement should be self-sufficient, just not with plots alone. Using a 2x2 square for water when a pair of tiny hand-pumps will do seems wasteful for 3 folks just trying to survive.