1. Don't know, don't have Virtue
2. Not crucial, but a great thing to have
3. I'm on 17, with a generous amount of leeway so I get no shootdown, you could probably pull off 10-13
4. I wouldn't, the EOS reg is fine, just needs a bit longer than usual time to break in, but if you'd like, you could.
The reason I say leave it on is because it vents exess pressure, so if something horribly wrong happens, you don't blow your noid, or if you use CO2.