Wow, that's a nice looking machine. How tight are those SBR20 blocks?, I've found the 16mm ones to be quite nice out of the box, even better than the SBR12 even with the latter having adjustment screws to fine tune. I'm tempted to get a kit like yours, but I'm lacking some feedback on these blocks (I want to cut aluminum with a precision of at least 0.1mm, hopefully 0.01mm).
How thick is your gantry's aluminum plate? are you getting any bending?
BTW, your machine remembers me of this one: