1: Since it is just you
Keyboard Maestro is engineered by Stairways Software Pty Ltd and fulfilled by FastSpring. Keyboard Maestro is licensed on a per-user basis and individual users may use it on up to five Macs.
So you can install Keyboard Maestro. On BOTH computers, and each can have its own custom macros
2: This may be of interest
Then PM the two KM users in that thread
3: Forget about KM, once you are on the subPC , how do you get back to main PC?
4: Suggest you raise a support ticket with Synergy help and just take my approach to start to keep it simple
5: It may be a question of doing TWO steps
Transfer back from subPC , then switch keyboard layout?
6: I cannot access any manual or detailed documentation on the synergy website. Is there a pdf you can send/link to?