Gtrx, there's an omission in your base kit. You included a second 1u Ctrl instead of a second 1u Alt. This means that Mac and some HHKB users won't be able to cover their bottom rows correctly (it requires 2× 1.5u Super and 2× 1u Alt), unless they use Meta keys. It's still not too late to fix this mistake, though; you will likely be able to talk to GMK to have the second 1u Ctrl key replaced with 1u Alt (without altering the quotes, since the number of keys stays the same and all key sizes stay the same).
Edit: To be clear, it's not like the second 1u Ctrl is useful to begin with. No modern ≥60% layouts use two 1u Ctrl keys.