Runes & Masteries

So as i play i need to have a bunch of both pages set up, one per character i play. if i play howling abyss and get some one i havent played what do i do? what im asking is there a main set of both pages i should have and use as per who i want. like a support, adc, ect.

side note. why do i have to wait until im lvl 25 to use team builder? (from lvl 14 it looks like it will take weeks with my play time) what is the benefit? how is it different than blind pick or draft?