I think Silverback got it right with his comments. He made you a mighty good offer too. I'd like to add a little to it for you. If you want to see what it looks like in green then spray it green. The painter shouldn't care and if he does there's nothing that says you can't sand it off before you send them to him. But just to save you some work, almost all of that rattle can paint will wipe right off the parts with a rag and acetone, which is good because rattle can paint is generally hard to sand off, it clogs up paper badly. Standard automotive paints and painting technique are superior in every way. But you have to pay a bit for it.
You can put decals on top of or under the clear coat. If you want to do it under the clear coat what you want to do is by an extra decal and do a test panel first. Spray a panel with your clear, put on a couple of coats and then let it set for a couple of days. Sand it with 800p wet paper and then clean it real good. Then apply your extra decal to it. Then shoot a good heavy coat of your clear over it. Now sit back and watch it. If it stays where you put it, doesn't crack, craze, curl up, run, or turn strange colors then you're good to use the other ones you bought.
There is a side benefit to putting decals in the clear. It forces you to essentially do a flow coat job on it.
To do it shoot a typical 3 or 4 coats of clear on the parts and then let them set 24 hours and then sand them just like you were going to cut and buff them but do it to 800p. Then apply your decals. Remask, clean the tank (use a degreaser, your paint store will sell it by the gallon, its not expensive) and tack it and then shoot 3 more coats of clear on it. Then cut and buff it.
By the way, I very much like your choice of colors. I would suggest that you at least do a little pin striping somewhere on it to break it up though. If you do that take a look at a color wheel and spend a few minutes reading up on their use before you pick the color for the offsetting color.
