Congratulations on your new van hope it serves you well, and welcome to this forum. If you plan on adding anything such as a trailer hitch and light wiring if you don't already have that I would suggest doing the wiring before you add the shelves since access from the back to the battery compartment will probably be harder once you have them installed. I also have a bulkhead which makes that access difficult.
Personally I would think it might be a lot of trouble installing shelves from another van unless it was the same model but maybe I am wrong with that thinking. Building your own or buying shelves specifically made for your size van might be easier depending on your skill set. If I were building my own I would end up using wood since my metal forming skills are seriously lacking but metal shelves certainly have some advantages IMO. I think there are some threads in the how to section and other sections that should give you some ideas. Again good luck with your van and build projects.