build a gmaxx and i need help

[JoFreak]

It's OK that you ask all those questions, I did the same not too long ago, and if anybody is bored by the same questions over and over again, nobody is forced to answer them
Yes you would need the drive cups as they are for the center drive shafts.
The adapters for the driveshafts are included in the hybrid bulkhead set, so you can use stock traxxas driveshafts with your truck, which I recommend you do.
They are cheap, can deal with BL-power and can absorb shocks to the drivetrain better then steel or aluminium driveshafts which helps the diffs.

As for the arms I would take RPM or Flextek arms, RPM because they are cheap and can take a beating and Flextek because they are expensive and can take more beating
I wouldn't take aluminium arms though as in my opinion they are too stiff.
And get RPM axle carriers or stock ones, for the same reason.

Take the gorillamaxx chassis allready! Why? Because you can't decide and I like the G-maxx better

UE is Unlimited Engineering but nothing to think about any longer as they don't really produce anything anylonger.

As for the non-tranny-build: look at my thread and you'll see.
You'll need a centerdiff mount but with a mounting plate for the G4-chassis. But you have to ask Mike if he builds one for you.