you shouldnt, the 5100's in the front are stock travel length and the rear are only 8.8" or so when i measured mine when i took the out, but the rears very very close to taunt when fully drooped so it couldnt hurt to do the rears
No you don't need them with that much lift. I ran stock brake lines with 3" icon lift on my FJC for 6 years with no issues, even full flex