sounds like you need to weight it with a belly weight it is trial and error but most of the time the weight is put just in front/back of the hook hanger or were the hook hanger is
on smaller bait for longer baits in might take two or three to find out how much weight just clamp a split shot to the hook and try that to see if cures the rollout on your bait if works then drill a hole just big enough to put the split shot in and epoxy in place let it dry and fillthe rest of the hole withfiller and reseal the bait and paint,
as for paint all the ones you stated in your post will work,there all water base paint or you can go to wal-mart ,hobbie shop,craft store and pick up some foke art paint thats water base too and use that(its cheaper to buy then air brush paint) just thin/reduce it till its about like milk, as for colors get the basic ones like white,black,green,yellow brown becouse you can mix them to make about any color,you can practice on paper towel layed out on some cardboard to get a feel for your airbrushs then buy you a few differnt style plastic bait and paint them,you can wash the paint off if you dont like it and spray it again and again