Basement sub-panel wire requirements

[fordluver4x4]

I’m running wires to the basement for future basement finishing. I’d like to add two circuits of outlets (one on the finished side and one on the unfinished side of the basement), baseboard heaters (I’m also open to other heating options, the basement stays in the low 60’s in the winter, so I only need to raise the temp 5-10 degrees), and possibly an extra circuit for future use if needed. I figured on 6000 watts for the heaters (four 1500w heaters), and 3600w for the outlets (1800w x two). The run to get to the basement is about 60’ including up through the garage wall, across the garage attic, down the joining wall, and across the basement. I’ve considered individual runs for the two outlet circuits and the heat circuit (three runs total), or just running a larger wire to a sub panel in the basement. I lean toward the sub-panel for versatility and because I can install that now and then wire off it when I get around to finishing the basement, but I don’t know what wire to use. With my above estimates I’d need 9600 watts, which should be 40 amps at 240v. I’ve heard of an 80% rule where you can only use 80% the capacity of the wire, so do I need a wire rated for 50 amps? I also wouldn’t mind a little extra capacity in the panel in case I need it, but I think above 50 amps I’m starting to need a pretty hefty cable. So I guess my questions are:

1. Is there a better option than baseboard heat for the basement that would take less current (I don’t want to cut into the central air)
2. Do you think a sub panel is a better option than individual wires running to the basement?
3. If individual runs are best, what gauge do I need for the four 1500 watt 240 volt heaters (6000w @240), and how do I terminate that wire in the basement before I install the heaters?
4. If a sub panel is the best option, what size/type of wire do I need for 40 amps, and what if I want a little extra capacity (50 amps)?
5. Is it best to stay away from aluminum cable due to the extra size and trouble running through walls etc along with needing the goop to keep it from corroding?
6. Can a sub-panel have more amperage of breakers in it than the breaker/wire supplying it? IE: my main panel is 200 amp, but there it probably 4-500 amps worth of breakers in it (they obviously won’t all be at capacity at once).
7. Could I run 6/3 romex off a 50 amp breaker, to a sub-panel with a 50 amp main breaker, and have 12,000 watts (50 amps) total wired off it, or does that violate the 80% rule? (this would be two 15 amp outlet circuits, one double pole 30 amp breaker with the 6000 watts (25 amps) of heaters, and one 20 amp breaker left for future expansion).
8. If I don't want the extra capacity, could I do 8/3 romex with 40 amp breakers for my 9600w need, or again, does this violate the 80% rule?

Thanks for any help. Also, if there is an electrician in south central PA that would like to come talk over my projects, then double check them and hook them up once I’ve got everything run, I’d be interested in that.