I've used both XTC-3D and fiberglass resin I had lying around to fill in layer lines. Like the XTC-3D for parts that are printed in a translucent, but it's a little pricey per oz, so if a part is going to get paint, I prefer fiberglass resin. XTC-3D is basically a 2 part epoxy. Either way multiple thin coats with sanding in between will get you the best results for epoxy/resin layer filling.So far as the outer shell goes, I've seen XTC3D, do you have an opinion on that? The way I see it, I can add that as well to avoid a bunch of sanding, or use bondo if I need to.
Here's some finished gauntlets that used 2 layers of fiberglass resin(outside only), no bondo, and very little sanding. No sanding was done to fix little "shards" in the grooves due to a time crunch.