Tap the threads if you can. Particularly on the c-hubs. You can also use the longer ball studs with a nut behind. There's a thread about it somewhere. I also use an m3 washer on the ball stud which stops the non threaded part going into the plastic and forcing it open.
Never had a problem with the wheels binding on the plastic hexes. But now use the alloy ones as they don't come off with the wheels
Uprate the idler, and also make sure you compress slipper and diff springs prior to fitting. It's the overheating that usually damages the internals.
With the weight it's personal preference and also depends how much your kit weighs. Lipos, std/ low profile servo etc. with the xPro I have under lipo, under servo and the brass front bulkhead. Think its 60, 35, 30g weight.