There's really nothing wrong with using the PT, you're just not getting anything extra (for this app) for the price. The ACQ treatment will eat into the steel, but not before the board is long gone. It would take a lot of years. If you're worried about it apply some stick on flashing (Fortiflash, Vycor etc..) before the boards)
PT boards are soft. Typically they use a green Hem/Fir. They have to be soft in order to get the treatment to penetrate properly. A quality Doug Fir (not Pine or SPF) will be stronger. T&G is an option also, but the cost is a little more. Or if money isn't an option, Apatong would give you a lifetime deck (for the tune of about $1500) Treat the bottom and sides of the boards with a quality sealer (I use Penofin) before installing.
I use and sell a quality Coated Type F screw with a torx bugle head. You have to pre drill but they resist corrosion and are plenty strong.