If you’re mainly doing slides and film, get a slide and film scanner. They’re much, much, much, much better at scanning slides and film. All of the modern ones will even digitally remove dust from the image as you scan. Unless you have a $20,000 oil-mount flatbed, you’re just not gonna get the same quality with a flatbed as you would with a slide scanner.
You should always try to scan the negative or the slide if you can, as opposed to the print, unless you want to post-process it with some old fashioned dark-room work instead of photoshop work.
BTW, if all you’re planning to scan is Polaroids and stuff, you can pick up a cheap $100 flatbed that’ll do that just fine.
This will do you quite well for a slide/neg scanner:
Or this, if you have more money: