I'm planning on finishing a basement by building a stud wall inside my
poured cement foundations, then hanging drywall.

1) My building code requires pressure treated lumber for a baseplate.
Assuming I use a non-arsenic lumber like ACQ, are there any special
safety precautions I should take? Specifically, does it matter whether
I cut the lumber inside (where I can vacuum up the sawdust, but some of
it may get in my house) or outside (where the sawdust will stay mostly
outside my house, but get in my lawn, and where I will be very cold)?

2) I can't decide between spacing the studs 16" OC or 24" OC. As far
as I can tell, (a) 24" is quicker and cheaper; (b) 16" is better for
hanging wall cabinets; (c) 16" is more tolerant of errors and will make
hanging drywall easier; (d) but if I hang the drywall horizontally
instead of vertically, 24" is probably fine. Am I missing anything?