I just used traditional 2x6 studs and for screws I used 3” coated decking screws. I built mine years ago and I don’t remember how many boards I needed. I just drew a diagram so I knew exactly how many board and what lengths I needed.
I would strongly recommend against using pressure treated lumber. Pressure treated lumber is wet and wet lumber is more likely to bow and warp when it dries unevenly. If worried about moisture after the stand is built you can coat it with a weatherproofing paint, I didn’t though.