I’m building the international version. I can give you my feedback on the assembly process.
The first point you’re mentioning is not a big problem, the roller lock doesn't fit well but it does its job, just take care to don't screw them too much.
The middle Z parts are also a bit too tight, but the 25mm pipe goes inside if you push a bit, just don’t screw completely the middle screw.
The only problem I had was for the middle joiner parts. The 25mm pipe can’t go between the bearings.
To solve this I first cut the arm of this part in order to allow it to deform and to introduce the pipe inside, it’s ok but then after assembling everything, it puts too much strain on the Z axis bearings and the Z motor has to work much more than necessary.
So finally I moved a bit the bearing position of that part on the STL (-0.7mm) and I reprinted them. Now everything is OK. The middle end parts have the same problem but here again if you unscrew a bit the middle screw everything is ok. However I modified and reprinted these parts as well.
It's a bit of extra work but this project is really smartly designed. Congratulation again!