1) what is a good primer... Plastic or regular primer or does it really matter?
The best is a good automotive primer from an auto body paint shop... but if you want to use rustoleum you will likely be just fine... I have had good results with rattle can primer.
2) is it smart to buy the primer filler incase of any imperfections in the fairings this would help fill them in?
I use filler primer to cover any minor blemishes most of the time. If you aren't concerned about weight, go that route. On the tank I use self etching primer if it is bare metal.
3) where is the best place to buy supplies? I want to go flat black on the fairings and tank.
Any automotive paint shop, English Color is where I go down here in TX.
4) has anyone noticed a significant difference in rattle can vs air gun? Given environment is the same.
Yes, a huge difference. Not saying it can't be done with a can, but I personally can do 1000000000 times better with a gun.
5) can the same paint be used on the tank that's used on the fairings?
Here is my last paint job I did.. I will be doing at least 2 more this year.