I'm trying to get as much weight out of this thing as I can, but I need to keep it sealed until I can properly remove everything and weld in a sheet. In the meantime, I was hoping someone could tell me what all could be removed from the roof before it starts to leak. I have the headliner out, but I can't make heads or tails out of what is necessary and what isn't. Any help would be appreciated. Thanks!

 

If I were you I would just remove as much of the sunroof as I could by removing all the nuts, bolts, and screws it has then temporarily sealing it with a plastic sheet with duct tape. Won't look that attractive but at least it will keep the rain away until you weld sheet metal over it.

 

If I were in your shoes, I'd take the entire motor assembly and the tracks out. I'd then put the sunroof panel back into place and seal it with silicon or caulking, etc until you weld it up.
Matt