Over the years, I get asked regularly about best picture size, number of pixels, best DPI and so forth. The thing is, it doesn't have to be a mystery and once you understand some fundamental concepts, figuring out how best to size a picture or what format to put it in becomes fairly simple. The hard part is taking thirty minutes to an hour and doing some reading on the topic.
I've recommended this website for a very long time to people who seem genuinely interested in gaining an understanding of the technology.
www.scantips.com
It is written for the layman and written very well. It is not just about scanning, it is about anything to do with images, camera, video or otherwise.
That said, almost no one I recommend this site to ever goes there and does a little reading. They would rather scratch their heads, take their best guess or call me on the phone and ask. I've stopped asking them if they visited the site before they called. The folks on this forum however, strike me as people who have a desire to learn, or else they wouldn't be hanging around here. Give it a try, you'll learn something, even if you think you know it all already.