I don't have the exact number off the top of my head. But a quick search on manga forums or asking fellow manga enthusiasts might help you get the answer you're looking for.
Well, as far as I know, the Maximum Ride manga consists of approximately 8 to 12 volumes. But the exact number might vary depending on different editions and releases.
Not much. Maximum Ride is a story series and Manga Rock was a platform for accessing various manga. But Manga Rock was shut down for copyright issues and it's not a direct connection with Maximum Ride.