Fork bleeders are the same as a KYB (5mm thread dia.), larger than the WP units. Air filters won't fit, I can just tell you by looking.
All I've done to my Beta is carefully grease it, install heavier springs for my weight, have TwoWheels revalve my fork and install radiator guards, pipe guard and a BRP submount for my Scotts Damper I had laying around. Really don't know if the damper would be needed, if I didn't have it already. Heavier tubes are a good idea, but I really like the stock Michelins, especially the oversized balloon (140/80) on the rear. Jetting is stock, and I haven't messed with the PV adjuster yet either.
Fork springs from a Yamaha SSS fork like my 2006 YZ fit, along with KYB rear springs, although KYB's rears have a slightly larger dia. I do like that Beta already has all kinds of aftermarket parts available already, which I'll look at as I wear out stock parts.