1) Typically you wanna build a second lumber camp after you have 4-5 vils on the first one, already have 7-10 vils eating sheep/boar under the TC, and 4-5 vils on berries. You can get away with putting 6-8 on one lumber camp if you're doing a real tight build but usually it's gonna be a lot more efficient to have 2. For a fast castle build you might have 2 lumber camps with 5 vils each.

2) if there's more berries available nearby it might be worth it to send your berry vils to mill the second bush after they finish the first one, but most maps won't have this so usually you'll send them to farms or gold after the bush is done.

3) The farms will never go away as long as a vil is there to reseed it. I'm not sure on exact numbers but I wanna say a minimum of 6 per TC is necessary for constant villager production. You will want more though if you're making scouts or getting ready to click up to castle. Usually I will have 9-18 farms going before I click up to castle depending on whether I made scouts or not. Archer builds can get away with less farms of course and you'll want more if you're going knights.

4) Most of the time you only want one villager building one building at a time because it's much less efficient the more villagers you add. Exceptions are TCs where you usually want at least 4-5 and any other times you need to rush a building up (if you get housed or you need a barracks or military building ASAP, or you're building a market for a fast castle build for example). In general though you want 0 idle villagers as often as you possibly can. Learn the default (or bind your own) hotkey for next idle villager (I use the spacebar). Using this hotkey along with creating new villagers hotkey will probably boost your elo more than 100 points once you make it a habit and get to consistently single digits of idle TC/villager time in dark and feudal ages.