A) No concern with the integrated comp. The external comps do however allow for better gas expansion and therefore better recoil control.
No slide lock back is what you want in Open and other divisions so you have one less thing to worry about during a COF
C) You will likely, if you are like me, want at least a couple more 140 mm mags so you don't have to rush to get mags loaded between stages
Have fun, I love Open and don't see myself going back to the other divisions anytime soon.