Common mistake: thinking a great deal about Code bare minimums and the installer's convenience, and not at all about what it'll be like to live in the house later. We're the smart humans, electricity works for us not the other way 'round :)
Feel free to run "switch loops" (power to light spur to switch). You simply need to use /3 wire for the spur. This is no big deal. If you want a fan-light on a switch loop, consider throwing in conduit instead - EMT with metal boxes if that works out to be easy, otherwise smurf tube. That will allow you to run 4-5 wires if needed for full control + neutral.
As far as understanding switch loops better, I want you to use colored tape to override the default colors of wires. Black = always-hot. White = neutral. Red = switched-hot to a light. (and if you do "/3 switch loops" this happens automagically, no tape needed). Yellow = both 3-way travelers (there's no need to distinguish them from each other). Blue = alternate color for switched-hots or 3-way traveler pairs if you have 2 in the same box.
In choosing plastic vs metal boxes, remember the purpose of junction boxes is to contain serious arcing which would otherwise start fires in in-wall materials (where it's impossible to put out a fire early). Metal has the virtue of not burning, very high melting temp, good thermal conductivity to remove heat, and will also ground out a loose hot wire, assuring a quick breaker trip.
I believe pull-chain/bare-bulb sockets are no longer Code in closets due to the high incidence of them getting wacked and exposing conductors in broken bulbs, or of getting too close to clothing/bedding and setting them on fire. The best option is a switch working a low-profile bulbless LED fixture.
Given the efficiency of LED lighting, there's no trouble running all lights off 1 circuit and having a circuit just for lighting. However, remember if that circuit trips, the house will be completely pitch black. I prefer to plan it so if a room loses all lights, the adjacent room has lights. That said, your idea of having a room's one light NOT on the same circuit as any of the room's receptacles is a very sound idea, so that if you make a mistake in room 1, you have light to fix it.
The #1 design mistake people make is thinking in terms of "1 circuit per room" which is actually harder; it means encircling each room with wire. I prefer to run 1 circuit per wall and serve rooms on both sides of that wall. With some wrapping around at corner walls, this means typically 3 circuits per room. That does two things for you:
- It saves a lot of wire since you're not encircling rooms and having room A's wire pass right by room B's wire in the same wall.
- It means each room has access to several circuits, so when you designate one room the computer room and put 3 PCs and a laser printer and supplemental A/C in there, you can power all that. That's especially helpful with the kind of small business now possible thanks to the Internet; I know one guy who makes small-production model kits and has 3 laser cutters each driven by a PC humming 24x7. My way, no additional circuits are needed.
The kitchen needs 2 circuits that serve absolutely nothing except countertop receptacles, other kitchen/pantry/dining receptacles, a gas range, and a wall clock. Nothing else and certainly not a fume hood.
However you are allowed to have more than 2 circuits serving those loads, and that's a good idea to reduce the problem of the chef tripping breakers. MOST kitchen plug-in heat-making appliances draw 1500W, and 20A circuits only have 2400W, so 2 heaty appliances on any circuit is bound to trip it. That means in a bare-minimum-wired kitchen, the chef can't run 3 appliances at once at all, and if they run 2, they have a 50/50 chance of tripping the breaker. Having 3++ kitchen countertop circuits gives the chef more flexibility. The additional circuits (beyond 2) can indeed power other stuff.
Bathroom rules are complicated, but you can just follow the 1-bathroom rule of "A dedicated circuit that powers only one bathroom's receptacles can also power hardwired loads in that bathroom". The bathroom recep must be GFCI protected anyway, so you can just feed the tub light off that.
Here the common mistake is putting all bathroom lighting on the recep circuit and standing there in the pitch black holding a hot curling iron with no way to see where to set it down... but you know better than that, and there's no value to GFCI-protecting a ceiling light that is grounded. It's not like you're going to drop it in the sink lol.
