First let me say this site is very informative, thank you.
I am building a 3 season room in Northern Wisconsin and the customer has requested hickory 3/4" x 3 1/4" hardwood flooring. This room will not be heated in the winter, customer is a snow bird (lives in Florida in winter).

Here are the specs:
The addition is elevated by concrete piers over 6 mil vapor barrier and rock
Framing is 2x8 ACQ (treated) joists are 16" on center; parallel with existing home

3/4" T&G OSB subfloor nailed and glued
Floor is insulated w/R-19 fiberglass
Walls and Ceiling are insulated w/R-11 fiberglass w/plastic vapor barrier, walls are wrapped w/Tyvek on exterior

Here are my questions:
Any concerns with the lack of heating over winter?
Is it ok to put on OSB flooring (did not get wet during construction)?
Am I restricted to running flooring 90 degrees to joists?
What is the best Nailer/Stapler for the job?

Thanks in advance, Concerned Contractor

As long as the customer understands and accepts the limitations of a kiln dried flooring product exposed to temps and conditions outside the normal acceptable parameters. Hickory is not a very stable wood and has been known to expand and contract more than more stable woods. Being a fairly hard wood, tongues can split easily on nailing so care needs to be exercised when nailing. A Bostitch M111 FS or cleat nailer would be my choice. That floor should be installed at 45 to 90 degree angle to the direction of the floor joists. The subfloor needs to be within 2% MC of the hickory flooring so you'll need a moisture meter to check it. OSB isn't great but is accepted by NOFMA as a subfloor material. Make sure your customers understand the drawbacks of installing a wood floor in this situation and that they will not hold you responsible for their choice.