I think you have three choices that represent different mixtures of your ask.

1. Just scan them. Most phones have either a built in or app-available function to take the burdens out of scanning documents and photos. With thousands, you’d be talking about stretching it over a few weekends, maybe, but you could do it while watching tv or listening to an audiobook.
2. Scan and edit. You can buy a higher end scanner that would allow you to have more control over the quality of each scan. You could also use photo editing software to color correct or make whatever edits to the hopefully only dozens of photos you really care about, while leaving the option to do so open if you suddenly need that pic of Aunt May at the picnic.
3. Pay a pro to do it. You can find services that are all over the place in price and quality (basically because they’re centered around either option 1 or option 2). If you go with a higher end place, you’ll get people with a much higher skill set in scanning equipment and using photoshop then you. Lower end is basically lie the clerk at the UPS store that sends faxes. I’d recommend against sending any really important ones through the mail, though, so this again might be where you’d want to sub-select on the ones you really want done well and the others that you’d only mostly want to keep.