Hi Chris,
If you are going to do racing stripes or similar, I'd suggest getting an air brush kit, that way you eliminate the risk of too much over-spray, (no need to pre-sand or re-apply any primer, if it's going over fresh, dry and hardened paint) and you can lay the colour coats down as thinly as you need therefore minimising any edge lip, plus minimising the risk of pulling any colour coat paint off with the paper tape when you are finished, but using an air brush really depends on how steady your hand is. You use a pre-made, self-adhesive backed, stencil to give a clean, sharp edge definition, you can even hold it the stencil free hand if you are good enough (you remove it before the paint drys, so you don't get a edge lip), you don't have to apply as many coats either, just enough for the colour to be solid without seeing any of the colour beneath, through the paint. It's difficult to get a normal spray gun to spray a thin, light coat, whereas an air brush is designed for that specific purpose.
Even a good quality paper masking tape will allow the paint to bleed a little bit under the tape, as the surface tension of the paint is drawn to the edge, and it will also leave a pronounced lip on the edge of the stripe, so in a cross-section, the edges are thickest and the middle of the stripe is thinnest, sorta like a "U" shape, if you looked at in a cross-section. You can lightly sand the edges down if you are good enough, but if you do, you may lose some of the edge definition.
The alternative is to use a "sticker" type, self adhesive pinstripe / decal, the thinnest you can get, apply where you want it, (again no need to pre-sand or clean the surface if it's going over fresh paint, just pop it straight on, as long as the paint surface is thoroughly dry and hardened, for if you need to re-adjust the position of the pinstripe / decal and need to lift it off again, you don't take any paint layers below with it), then start applying clear coats with a normal spray gun, (not too thick as the thinners in the paint before evaporating may dissolve the adhesive or the plastic of the pinstripe / decal) over the top of the pinstripe / decal and letting each coat dry properly (you will get the same surface tension lip on the edge of the pinstripe / decal, just in reverse, as explained before) before applying the next coat, once you've got an minimum adequate thickness of clear coat, (you are supposed to be sanding the clear coat, not the pinstripe / decal, if you do, stop apply more clear coats and then sand, you don't want to touch the pinstripe / decal underneath, at all) lightly sand till the clear coat lip edges start to become smooth to the touch and in the reflection.
Once you are happy with the smoothness of the edges, start to spray each clear coat to the tape / decal area first, then widen the spray to include the whole tank, until you get a smooth, blended surface over the pinstripe / decal and the edges blended in, to check look in it's side-line reflection. Let thoroughly dry and harden overnight to allow for shrinkage, then see if the shrinkage has brought out the edge lip again, if so, go through the process all over again until it's right. If you don't do this, the clear coat's surface reflection will deform over pinstripe / decal, it will look like **** when it's finished, it's also pretty difficult to sand it out smooth, you want a nice even surface with no bumps over the pinstripe / decal in side line reflection.
Depending on how many clear coats you put on, will depend how much you've got to play with when it comes time to lightly buff a mirror shine to it when it's all finished.
Sorry for the long explanation, but I'm trying to explain, step by step, the process for doing this, as it's probably the one critical part of spray painting that is fraught with failures. If you know how to do it properly, it looks excellent, if not, it's not worth doing at all, as the results are shocking.
If you were in Aust., I'd do it for you or show you how to at least.
I hope this helps.
Mick.