Remix OS 3.0 USB Mode Questions

Looking to try out USB mode instead of HDD mode so that the install is more portable, and I just had a few questions.
#1 what are the supported USB stick sizes?
#2 Does USB mode require a GRUB loader, or can it boot on any machine (including Mac's) without any modification to the host system?
#3 Can you swap between computers without much issue, or do compatibility issues arise (even if functionality in the hardware is the same)?

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