More questions:

1) In order to add enough circuits in my breaker box, I may have to double up
some of the breakers. We had a new heat pump system installed and the HVAC guys
stole a lot of space!

I really only have one breaker space left, and 2 more circuits to run (1 20A for
bathroom and 2 15A for bedrooms), BUT some of the other breakers are single and
could potentially be converted to two small breakers. What are the rules
regarding this? I am wondering why some are single and some are double...why
not just make all of them double to leave space?

2) Does the bathroom circuit have to be dedicated to the GFCI outlet ONLY or can
it also feed the vanity lights?

3) Can NM cable be run diagonally under the joists, or must it follow the inside
of the joist or through holes? (remember I will be doing a drop ceiling)