What kind of microscope should be used to view biological structures (such as spores) roughly 5 µm in length?
I think you have a good question, but if you want to get a good understanding of the issues you raise with it, then you really ought to consider spending some time reading this optical microscope primer. In my opinion, you need not bother with taking an undergraduate course at a physical university. As an intro to biology (which is not really necessary if all you want to do is look at small things in a microscope and understand what you're seeing), you might want to consider enrolling in this free class, but if all you want to do is look at small things and have a basic understanding of what you're seeing, I think all you need to do is read the primer.

If it was me, I'd read at least some of the primer before investing the money in a microscope. Otherwise you're just taking a blind leap of faith from someone's (perhaps biased) suggestion.