Few questions, need answers !!

Hey im running a FP Mara to see how its working and I rarely crit and just wanted to know why

How much crit do I need to crit every hit/ two hits ?
How does GMP/LMP effect crit? GMP = crit chance x4 ?
I also want to know what the chance of fusing a 5l is just curious^^

Hope someone can answer my questions!