i see a guy on craigslist has some 15/16 maple gym flooring for sale at $2sf that has had all the nails removed. how hard will this be to install? i assume i can just shim my nailer until i get the staples to go in the right area of the tongue. anything i should look for or be worried about?

Check for straightness, water damage, split t&g. Yes, just a matter of shimming the base of the nailer.

how hard is it to install vs 3/4 or 1/2? my brother thinks im crazy and going overboard with 1" flooring and that I may have more trouble installing it due to the thickness. the house is 100 years old so it may have some slight unevenness in the floors. I just bought the house and have yet to close on it so its a little to early to take a level to it yet for the most part they seemed pretty level to me for a really old house.

IMO the thickness doesn't necessarily make it harder or easier to install. With a thicker would you can run against transition and other height issues.

The subfloor will need to be flat( 3/16" within 10'), and of adequate thickness and material to fasten the hardwood.

You can purchase the wood, just keep in mind it's possible you may run into some substantial alterations for it to work in the house. Personally I think your putting the cart before the horse, just sayin.

I know the subfloor is a 6" wide plank. how thick does it need to be in able to nail a wood floor to it? i have not had a chance to measure the thickness as the subfloor has a 1/2" thick mdf floor over it that i need to rip up. Just want to see if its within spec to be nailed to or if i need to plywood over the top.

The subfloor should be 3/4" for naildown, and not particle board or MDF etc,( but sound like no problem there). It's possible what you have is 1" x 6". It's possible they sheeted it out with the MDF due to flatness issues. If that's the case...You may need to sheet over the top of the subfloor with 1/2" plywood, after you tear out the MDF.

If the plank subfloor is adequate for a naildown, but not flat, depending on the condition, it may be possible to flatten within spec, and install the hardwood perpendicular to the plank subfloor.