Do NOT get one of the nail guns you have to hit really hard. The ones you hook up to the air compressor are the best.
If it were my house, I would use 3/4" wood. It's solid stuff. I worked for a general contractor for 4yrs doing interior remodeling. I've done a number of hardwood floors, and the kitchen/living room in my own home. DON'T go to Lumber Liquidators for your wood. I've had nothing but baaad experience with them on every job we used it. I have 3/4" red oak in my house.
Make sure you chalk a line down the room so that you have something to measure off of to make sure all your rows (especially the first few) are running true.
Prep the subfloor. Make sure all nails/staples are out of the subfloor/floor you are covering. Also, get rid of any existing 'lips' before you lay the hardwood. You'd be amazed at what you notice after the floor is down.
You can use red rosin paper like above, or you can get a roll of tar paper. Don't overlap the tar paper or rosin paper. Again, the whole lip thing. Staple the paper down to the floor before you start running the wood.
As a general rule, we would make sure our joints weren't closer than 6". It keeps the floor looking nice, as well as holds it all together much better.
Get a flush cut/undercut saw for the door jambs. Don't cut the wood around the door jambs. Grab a scrap piece and mark how far up the jamb/door trim the wood goes, then give about 1/16" or so extra so you can slide the wood under what you cut out. It's a much nicer look.
On your first few rows, you'll notice that you can't use the pneumatic floor stapler because the handle hits the wall. You'll need a finish nailer for that. I always shoot nails straight down on the ends of the wood, but only the ends against a wall lol. The rest of those first few rows, just angle the gun at about a 45* angle, on top of the tongue and fire!
You want to have the groove against the wall you're starting on, and the tongue side should be seen as you are laying the wood. Reason is b/c that's what the pneumatic floor stapler needs to staple the wood down.
I think that's it. Lol.