Upgrading cyma mp5

[-Jazzman-]

Hello folks ,

I'm from Belgium and since there are very few good airsoftshops and mechanics around here , I'm want to get into the upgrading myself.
I'm pretty sure i can upgrade my gearbox and get it back together , but any usefull links on how to do it step by step are welcome.
Anyway , I was thinking of getting an Guarder FTK m120 to put in there.
Are those gears that come with it any good ?
Is it any good overall, and where do u lot suggest to order ?
I got a 6,02 TBB in it , and an SRC metal hop-up unit.

Thanks in advance ,
Grtz,
Jazzman