Body repairs on fiberglass are really not that difficult. Of course, that depends on teh repairs needed

by the time you have finished building a kit car, you'll know just about everything there is to know about repairing fiberglass so it's a no brainer.
As far as WHERE to go... any bodyshop will have the knowhow to repair fiberglass.
Having a good kit manufacturer or source for those parts is important if you loose or have to replace an entire panel. Another good point of the Mirage argument... the finders, bumpers, fasicias, etc are all separte parts so if you need one replaced, you don't need the ENTIRE clip!
As for using authentic 355 parts, depending on the kit and what part you are replacing, YES. With IFG clones, the entire front and rear ends are a SINGLE part, so you could not replace any of those parts but perhaps a mirror or other smal part.
Speaking of which, I have real 355 mirrors on my car as they are "break away" mirrors. That means if/when they get bumped, they collapse rather than crack or break off. The 355 mirrors stick SO FAR out to the sides that they are BOUND to get whacked in a parking lot someplace.
Good question

DKOV -