First of all, punctuation man, punctuation.
As far as bikes in general go you can move and fire 1 weapon per rider, and this weapon can be heavy or rapidfire even up to full range and you can charge in the assault phase. For Ork Warbikes it means that you can move 12", fire your dakkaguns, and charge. You cannot fire both the dakkaguns and the slugga because that would be firing 2 weapons.
Warbikes cannot have the red paint upgrade, that's for vehicles only (vehicles in 40k terms mean they have an armor value). You'll see the red paint upgrade in teh unit description.