Seeking Flex Q/Ranked 5's clarification from a Rioter

So, since FlexQ will be in the same queue as 5's, I have a few questions.
Will 5's teams only get matched against 5 man flex queue teams?
While playing on a 5's team, will your flex MMR be affected? I want to be able to play with lower elo friends but don't wanna destroy my flex MMR.