Things missing from this kit:
1) If you're going to bother with an ISO enter key, you need a 1.25u Shift and some kind of extra home row alpha key, either the UK hash-tilde or backslash-pipe.
2) You have a numpad minus key in the R3, but in order to actually use that, one also needs a numpad plus key in R2.
3) I highly suggest adding a second 2.25u Shift for the purposes of 660 support as well as Alice support, since convex spacebars of the right sizes appear to not be an option.
4) R4 1u Backspace ("Back" or "Bksp") is worth considering if you're aiming to support JIS physically, which appears to be the case.