I would personaly apply 2 coats of resin, and 2 layers of fiberglass. This will make it much stronger.
I think you are supposed to bondo it, then sand and detail, then primer and paint. DONT FORGET TO DETAIL! Many people don't add detail, and it ends up looking like crap, or not all that it could be.
You could use resin over the Bondo as a cheap smooth layer, but it is NOT recommended, as it is hard to sand and is not necessary if you do some sanding on the Bondo. It would only be aesthetic if anything. It would do nothing for the strength of the armor either.
Fiberglass the inside with an additional layer of resin on the inside
Do a basic sanding all around
Bondo small parts at a time, dabbing on more bondo than needed to 'chisel' away for details
Sand with fine sandpaper
Metal glaze parts that need to be smoothed out further
Add LEDs, visor, cooling system, etc.
And that's pretty much what I plan to do. It also depends what helmet you're doing, if it's Flying Squirrel's or Slyfo's, you might not need to add a lot of bondo for anything other than smoothing things out. You might even be able to go straight to metal glaze or fiberglass jelly (if you're doing that sort of thing.)
Dark Rogue, I took a look at your helmet WIP and (no offense meant at all) but what you did with the bondo...is not what you want to do. Check out my Q+A topic in Creation>Pepakura for my REALLY LONG bondo application explanation. You'll see it b/c it's a REALLY LONG post. (maby on 2nd page IDK). Dabbing Bondo is sorta counter productive to smoothing the helmet.