I ran a standard spring and buffer in my 6.5 inch but found that the bolt was cycling too fast and was causing the trigger to reset so hard it was beating up my trigger finger, I switched to a Spikes T2 and problem solved.
You don't need an adjustable gas block, just try it with a standard carbine spring and buffer then change things if needed. PSA may have tuned the gas port size to run standard equipment so I would shoot it first before buying a bunch of stuff for it.
Another option would be to contact PSA and ask what they recommend for use with that upper.