i used to have a Pmod account once, iit was F2P. (it got demodded rofl)
there's no fixed amount of reports you need to get in order to become a Mod, basically what you need to do is report every rulebreaking you do.
having a clean offence history also helps, as im doubtful they'll allow you to ba a Pmod if you got busted for botting or scamming for example
additionally if you are a Member, posting helpful comments on the forums helps.
also very important- good ingame grammar helps, they would hardly let someone become a mod if he types like a 6 years old
bottom line be patient, there's no fixed formula to becoming a mod for what i know