I have Skydex pads in my ACH (MSA TC2000) and they are my choice of the three brands I have tried (MSA, Oregon Aero, Skydex). They are more comfortable, but the stock ACH pads are fine for you.
The strap that comes with the Skydex kit is dogshit.
The strap you posted a link to is the same one issued on BAE Systems (SDS) helmets and is what I use. The nape strap is less rigid than the one on the MSA unit but it's still a comfortable piece. It uses folded nylon webbing straps in lieu of the plastic P clips of the MSA helmets to hold the ladder locks for chinstrap adjustment. Some see this as a plus because the P clips can break with hard use.
Alot of guys like the new Headloc straps from OPS Core. I haven't used one in any capacity to give a review, but they look nice.
As for comms, I used a Peltor COMTAC-based comm headset in Afghanistan under my ACH with great success. For airsoft, I like the Cavalvy Elite II headset (airsoft guns are a little quieter than real ones).
Now, this is all ACH/MICH/TC2000 series based info.
If you bought a PASGT (not PSGAT), sell it and get something better. If it's for airsoft, get one of the helmets from Gearbox Airsoft.
I've seen a riot shield used well in one airsoft application only - Nil8r in the turret of a HMMWV. For anything else there isn't much point.