Best way to create large hi-Res AO size prints?

I want to create some very large (AO size or larger) (33" x 46"?) prints of interiors and possibly from a trip to Egypt.

The two ways I have thought are -

1. Nikon D800 with high quality lens. (Probably turning the camera through 90 degrees and creating a series of photos that can be 'stitched' in software to make very high res.panoramic shots)

2. Large format 5" x 4" camera with a wide angle lens around 90mm. Obviously there's then the cost of getting the transparencies scanned and digitized.

If I go for option 1 -
what focal length to use to take each photo to make the panoramas? 35 - 50mm?
Best quality lens to use?

If I go for option 2 -
How much $ for a reasonably good 5 x 4 camera and lens?
How much $ to get each transparency scanned and digitised? Would it be worth buying a scanner?

I have considerable funds and I have thought about medium format but the cost is astronomical.

Answering only part of your questions - shooting 4x5 on a high quality color transparency film and getting them scanned seems to this old timer a high quality choice but I lack information on the maximum image pixel count of the D800. For acceptable quality print of 300 dpi, your images will need to be 9900x13800 pixels - can the camera do that?
If you are going to make the prints you will be using a commercial print firm and probably a large flatbed inkjet print - you might ask them about scan costs of a 4x5 transparency or negative for best results. I think you will have to do quite a few scans to make buying a 4x5 capable scanner at that resolution

A 4x5 is going to a lot to lug around on a trip to Egypt. Before you decide, what gear do you now own? I recommend taking the best quality shot that you have from that gear and pay a professional lab to blow it up to the size that you want. You will probably be surprised at how good the resolution will appear. People often make the fundamental mistake of thinking that one needs 300dpi for every single print. They're wrong because large prints are best viewed from large distances. Walk up to a billboard. Do you think it was printed at 300dpi? More like 50 at best. The controlling factor, as always, is human visual acuity.

Unless you're a pixel-peeper. In that case, ignore everything that I have written. Continue to live in your world of dismay and drained bank accounts.