I have an Epson V500 attached to a Vista 64 machine.
I have some old family photos that I want to scan. the most valuable to me is an 8x10 B&W (sepia look) photo of my father taken in 1941 in his Army Dress uniform before he was sent to be oart of the D-day invasion.
My question is the correct resolution to scan. I scanned the photo and got a good scan but the file size is 1.2gb!!
I Scanned it at 2400 dpi.

What is the best combo for the best scan and a reasonable size file??

You need to consider some questions first. Yes, 2400 ppi is waaay more resolution than you probably are going to need.

I presume you plan to make copies? How large? If you're just making more 8x10's, 600 ppi is plenty. You could make a decent 16x20 at that resolution.

Any more resolution than that, and you'll be scanning a lot of paper-surface artifacts into the image file.

Yeah, and you can probably get by with even less. Your average photo print contains about 350 dpi of information. But better to overscan a bit to make sure you don't lose any.