resizing large scale

The math doesn't quite add up as mentioned but lets's assume you're working towards an 8x10 final image.

Depending on the original image quality, hopefully, it's something in the realms of 8000 pixels width, anything smaller will of course cause the image to pixelate more, regardless it will be somewhat pixelated anyway as your clients will walk right up to it as you mentioned. keep your PPI high and any over text on I would create as vectors in Illustrator so they can scale with no problems.

keep your PPI high and any over text on It  I would create as vectors in Illustrator so they can scale with no problems.

it would seem the only way you're going to do this is as you already mentioned; which is scaling the image up, cleaning and smoothing out what you can.

I would say if the image is any less than 6,000 pixels width then you'll need to ask your clients to reconsider the canvas size or re-take the photo.

You just set the required dimensions without "resample image" checked.

You normally don't resize, partly because it doesn't do anything for final quality, and partly because large banners are seen from much farther away. The optical resolution thus stays the same whatever the physical print size.

IOW the bigger it is, the lower the ppi. Same optical result.

Naturally, you'll want a decent pixel size to begin with, something around 6000 - 8000 pixels long side. A good DSLR will give you that. Such a file will work at any size, as is.