1. No idea, but I think either one would be workable. If you drill into the middle of the web of the frame members there will be a lot less weakening than if you drill near their edges.
2. I don't know that it's the best, but Gorilla tape holds up a lot better than Duck tape. Aluminum foil tape for ductwork (which is quite different from duck tape) also works pretty well. If the support structure is angles, you could put the angles on the outside and then use some sort of caulking compound to seal the angle to the coroplast.
3. I'd think aluminum angle would be quite sufficient, but either should work fine. The insulation and chloroplast are not that heavy, and are reasonably stiff.
4. Seems like a good idea to attach them together. Make sure that whatever adhesive you use is suitable for the foam panels; many are not for use on styrofoam. A construction adhesive (liquid nails sort of stuff, applied by a caulking gun) would be a good option, again making sure it's safe for the insulation you use.
Also, give some thought to allowing for later access to things that might need work underneath without having to destroy your enclosure; it may be useful to add an access panel or three. It might also be practical to just cut one when it's needed. At the least, taking some pictures of what's about to be hidden could pay dividends later.
