When you paint you apply a layer. Let it flash, usually for about 15-20 min. depending on the manufacturer. Apply anouther, let it flash, apply anouther, let flash, and so on.
I was planning on color sanding but never got around to it. Even if you aren't going to color sand the finish I would prefer to have one extra coat of clear (so total of 3) to allow for scratches to be lightly sanded and buffed out.
Take a look at custom paint jobs. 30 + coats of clear are not uncommon. Mind you they are applied a few at a time sanded then more applied. So unless you are putting on tons of clear at a time the clear does not become more brittle.