Hol Chan can get a little crowded, shark ray alley is just a sandy area where you hop in the water for about 10 min. or so & play with the rays & nurse sharks, they usually stop there on the way back from Hol Chan.
A good spot with less crowds is Mexico Rocks.
Stayed at Blue Tang last Jan. going back Jan.29-Feb13, You picked a great place.
There is a paper back(San Pedro Cool) by Lan Sluder, you can get it on Amazon $14.95, It is very informitive & will tell you every thing you would want to know about S.P.& all the tours