Is there a reason you're doing this by hand? If you were to take an image, project it onto the DiBond and start tracing, I'd worry about consistency, spacing & scale. I've done a few things on a flatbed printer that'll take a 4x8 sheet and would recommend that route.
A single D800 shot over 8' gives you a 76.67ppi, UHD (3840) over 8' gives you 40 ppi. Neither of which will look good, in the 4" - 12" viewing distance. If I were looking for perfection, I'd have it printed. If I were looking for art, the tracing & imperfections would play into it.
If you do the slide conversion, go for a 612 or 617 size as you will need as much detail as possible.