Depends on the specific school. Check the school's instructions. Is there a max # of LORs? If not, it's probably okay, although I'd personally limit myself to 5 letters. Remember, if you send too many they may simply read only the first 3-5 listed and ignore the rest. It all depends on the school but some may not bother to read all of 'em if you send them too many. I'd just pick the strongest 3-5 letters personaly but that's just me....