PK50XL2 flywheel and airfilter for D.R. 75cc

Hi guys,

I just bought an PK50XL2 for my girlfriend and I hope you guys can help me out. The flywheel has to changed  but I honestly do not know enough about the flywheel in general. I have noticed it is hard to find a flywheel for this model, but should I go for the lighter one or a "normal" one? I want to order the D.R. 75 cc cylinder set and a sito exhaust with the open manifold stub. I also want to change to the 16 sprocket primary driven gear. What kind of airfilter should I go for? Would the Polini racing air filter be a good choice?