These are very good questions. You (and others) don't know at this point, but one of the next posts will show Reflectix placed over the poly-cyan board and wood framing.
I have considered both aluminum (duct) tape, the thin stuff you describe, not regular duct tape (like Duck Tape brand), and I have considered vapor barrier tape (such as Tyvek house-wrap tape). In the end I have decided against both (even over the joints of the 4' wide Reflectix. I think a post soon will include both the reasoning, and a link to the report I found that helped me conclude those choices. These matters deal with air-infiltration (drafts) and water (both liquid and vapor) intrusion.
My mapping will likely depend on my photos history (threads are being saved in .pdf and will be printed out and end up in a book - in addition to digital retention). Now that DD is grown up, it's unlikely she'll record over my historical record to save boy-band videos or "Full House" as she did with my home addition video tape in an earlier era.
And speaking of solar on the roof, today's efforts are evaluating exactly that subject (placement), as well as removal of the work directly above the propane compartment to install a support backing-board in the bathroom back-wall that I forgot about until now. So that's going to put me behind a few hours to a couple of days.
