I've just finished framing out my basement to double our living
space. It's new construction with just a large poured rectangular
concrete floor between cinder block foundation walls.

The walls turn out to be just shy of 8' from floor to ceiling. I plan
to put in a suspended ceiling later so as to be able to get to all the
wiring/plumbing if necessary in the future.

My question is: Should I hang the sheet rock vertically or
horizontally? I've been careful to make sure that all the studs are
exactly 16" on center. I've heard that horizontally produces fewer
joints, but that also produces those nasty hard to hide 4' butt
joints. If I hung vertically, every joint would be flush.

Many of the walls are longer than 12', and since it's just me doing
the work, I don't think I have the strength to handle sheets that big.

I'm planning on doing the hanging and then bringing in a pro to do the
mudwork.

Related question: Should I hang the sheetrock a smidge - maybe a
half-inch off the (concrete) floor, just in case of water leakage?

Would horizontally hung sheetrock make for a stronger wall?

Any other tips?