I always put decals over a glossy surface as well....while some subscribe to the notion of then putting another gloss coat over the decals, I only do that if I plan on doing a wash on the item so the darkened lines show up over the decals, otherwise I skip the 2nd gloss coat and move straight to a flat coat.
You sort of need the 2nd gloss coat to do a wash, as the gloss coat lets the wash flow into the recesses, a flat coat will disperse the wash all over.
If you are doing dry pigments/pastels, you really need a flat coat so the pigments/pastels have something to bite into and stick. Common sense says that you should then put a clear coat over the pigments, but that can have an effect on the pigments that may cause them to disappear once the clear coat is on. You can always over do the pigment layer, with the hopes that putting on the final flat coat will dull the pigments back to what you really want, but it is a delicate balancing act.
For me...usually the pigments are the last thing to go on, and normally after that I don't do anything as generally the kit isn't going to be touched or moved that much, lessening the pigments rubbing off.
Of course using a Pigment fixer over your pigments will pretty much "lock" them in and keep them from being rubbed off as well.