Nothing. There is no subscription and no notice period. You only pay for the trip, directly to the coach company.
No. Everyone sees the same prices in the same order, with or without an account. The account is there for convenience, not for a different price.
You and your colleagues on the account. A coach company only sees your name and billing details once you request a booking with that company.
Yes. Your billing details go with every booking to the coach company, which sends the invoice itself.