Any type of LEED AP can qualify the project for this credit, but a LEED AP with a specialized operations and maintenance credential (LEED AP O+M) would be the ideal choice for a LEED-EBOM project.
While you are not required to prove that a LEED AP has been integral to the project team, a LEED AP should be significantly involved throughout the project.
If RECs and offsets are purchased at the corporate level, the owner can apportion any part of that purchase to the project building as long as it is not also credited to any other LEED project.
Solicit multiple proposals for the purchase of RECs and carbon offsets to ensure competitive pricing. Pricing can change rapidly as markets change, and will vary from provider to provider.