I think you would benefit from reading through the existing documentation.
You direct calls through a specific service provider (SP1, SP2, SP3, SP4) by typing **1 (or 2, 3, or 4) in front of the number, and you can only use the service providers associated with the physical port as you noted.
I don't know what "When I pick up the physical phone device tied to EP2, the receiver will be able to see my GV number" even means. If you make a call, you put it on a service provider with the prefix as stated.
If GV1 is in use, then yes, GV2 does the secondary action as you noted.
You can put rules in place all over the place - but the easiest thing to do is in the GV interface simply uncheck Chat when you're going out OR if it's a regular schedule you can set that schedule in GV, so it rings your cell between 8 and 5, but not the house phone, then rings both till 11, then doesn't ring the cell when you're sleeping. Lots of options, all in GV. Lots of GV documentation on their site.