Need adv. help with modding Maxii

Hey guys, whatsup? I'm new to PBP and signed up because I got my first pocket bike less than 3 months ago. My friend sold the MiniMoto Maxii to me for 40$ and it was a rundown, cracked bike when I got it. This was after a year of use from him. I modded it to some extent - throttle control was broke in half - taped back together (now it starts going when I turn the key [super glue doesn't work]) I took off all the yellow plastic framework that was not needed, and took the bike apart. After maybe 20lbs of unnecessary plastic was off, it would go at top, maybe 15mph. From reading some forums on here, I was thinking about getting a new controller, new motor, and new sprocket to make it go at least 25mph. As was already discussed, arpoldan said 750mW would work fine as the motor and a 55 tooth sprocket would be ideal. Though this was to a beginner, I was wondering if it would do any harm to upgrade to a 1000mW motor for a 36V bike. Maybe more. Please, suggestions would be greatly appreciated and if pics are needed, I'll post some. Thanks.