The absolute best platform for an SBR 9mm has to be the Colt 9mm
Its by far the best functioning system and since they already sell a SBR barrel for them, its a no brainer.
I've seen people put mid or even rifle length ff tubes on a 7.5" 9mm barrel. This covers a suppressor very well. Looks pretty cool when its done too.
ADCO does a great job cutting barrels from what I've seen.
As you know the 9's dont use the gas system so barrel length is not a factor when it comes to function. A very heavy buffer will cure most short stroke and bolt bounce problems with the 9mm's.
I recommend the RRA 9mm buffer as It seems to work best with the colt setups. Bolts for the 9mm are proprietary to the manufacturer of the barrel you go with, so thats not an issue either.
YHM makes a sweet mag block that allows the use of unmodified UZI mags. Its about 75 bucks IIRC and works very well. As for magazines GOOD uzi's w/ out cracked feed lips and the colts are the best.
There is no special requirement for the upper unless you go with the oly/vulcan/asa style 9mm setup, then it would require a hole drilled in the upper to allow for the ejector. The colt/rra style needs no receiver mod. You however may decide to tap the gas port hole and thread a set screw in to keep gas and dirt from getting out, and in.
Should be a pretty sweet setup when its done!
Good luck,
Matt