Lighting wiring questions 101

Forget switch loops, those went out years ago. If your wiring layout would be happier with "cables running off to switches" like a switch loop used to do, pick up some 14/3 cable to run neutral and hot to the switch, and carry switched hot back from the switch. You'll need that for cabling between any three way switches anyway.

1: Code doesn't give a fig if you run a dedicated lighting circuit or not, so long as you meet code minimum provisioning. My opinion having grown up in a house with shared receptacles/lights is that a dedicated lighting circuit is far better, people who have not had that experience often think otherwise. You do need to provide 3 VA per square foot for "general lighting and receptacle loads", but code does not specify how you split up that 3000 VA (25 amps) for your 1000 square feet. These days you probably want a good deal more for receptacles and don't need a huge amount for lighting unless you abhor efficient lighting.

2: The required 20 amp bathroom circuit cannot* be used for lighting. (*if it serves only one bathroom it can)

3: You don't need a separate circuit for a GFCI. Just put a deadfront (no outlet) GFCI on the bathroom lighting feed. That can be fed from the lighting circuit if you choose to use a lighting circuit.

4A: Code doesn't give a fig how you arrange the wiring, just that it meets code. You can wire it 17 different ways that all meet code. None of them are more right than the others. What makes sense tends to depend a great deal on the actual physical layout of your walls, switch locations, and light locations. Lights need switched hot and neutral. Switches need hot, neutral, and switched hot. How they get there is up to you.

4B: You CANNOT pull from the dedicated countertop circuits NOR from the dedicated laundry circuit. Those circuits (and the bathrom circuit) also do NOT count towards the "general lighting and receptacle loads."

5: see 4A.

In addition to all the points noted by @Ecnerwal:

1 - I highly recommend both keeping the lighting separate from the receptacles and having 2 lighting circuits, with alternate rooms on each circuit. That way if you have a situation due to either planned work or a faulty fixture or other problem, you are not (literally) left in the dark.

2/3 - Put the shower light/fan on a separate circuit. Lights/fans generally do not need to be GFCI (key exception if they are above shower or tub), and in any case you do not want them on the GFCI-protected side of bathroom receptacles because then a GFCI trip due to a wet or faulty handheld appliance will also turn out the lights. But I would put the light/fan on a dedicated circuit (not shared with anything else in the bathroom or with lights elsewhere) because that will keep open the option for a heat fan without having to run new wiring. (Since you are redoing everything, new circuits right now are cheap. Later after you have everything patched up, new circuits become much more expensive in time/labor/etc.)

4 - You can share the lighting with receptacles in most rooms - but don't. Make two separate lighting circuits - that way you always have some light, and you also avoid any work on receptacles causing lights to go out in that room. The exception is the kitchen - the kitchen countertop receptacles are supposed to be only used for that purpose and not shared with other stuff (there are some minor exceptions) - but again if you have separate lighting circuits you avoid the problem altogether.

5 - Splice in the switchbox. Think of the switchboxes as if they were daisy-chained receptacles, just with the switched-hot/neutral from each one branching off to the switched lights.

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 :)

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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.

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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.

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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.

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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.