@ Xenolance
Interesting how the kits differ, my layshaft needs quite a few shims to get it right whereas the kit you built didn't. My spur doesn't touch the upper deck though. I believe I had the same issue with the steering, part of it can be fully tightened but the other part cant. Don't think I had any play on the posts though - I'll double check in a bit. The suspension pivot balls do feel a bit tight to start with, although I put a decent amount of grease in there and played with them for a bit and they loosened up a lot. Agreed that it's worth looking for some metal ones. I think with some of this kit is really tight from new, few runs it'll sort itself out.
As for the upgrades, my first thought was the hexes when I finished building it - had some bad experiences with plastic ones back in the day so they're on my list. Probably going to get the servo mount and a few other bits and pieces - roll bars are the other one I'd recommend right away.