Yes you can.
The only thing is, I’m def not gonna get the kind of psi I’d need for surface cleaning with that low of horse power, but I’ll have the volume I’d need for house washing… lol.
Yeah right now I run two 5.5s with gx390s and I’ve thought about putting an 8gpm pump on one for rinsing when we do condos but I’ve yet to try it.
Yes…you’ll be around 1700-1800 psi.
No on the concrete…unless you pre treat and post treat at 4%