F or M if previously employeed

i've been working in china as employee (Z visa and working permit) which expired, I got Tourist L type, then again an other Z type and working permit.
Now, after the expiration, I will cooperate with a chinese company which does not employ me (and doesn't pay me any salary).
Which visa should I ask? F or M? can I get a 6 months type? How many days I can stay in PRC (at least 90 days without leaving the country)?
The fact that I was employee before, does it affect the chance to get a 6 months F or M type?