Hello,
1) EdgeOS runs on mips platform for generic x86 you need VyOS
2) Not sure about EdgeOS, in VyOS support for v6 added in betas of 1.2
3)GUI, maybe some other integrations with unifi, or other ubnt software and hardware, also starting from 1.8 in versions for EdgeRouter Pro other routing engine used to provide MPLS. But i'm not an expert in ubnt