You guys are probably tired of seeing my responses ;) , but there was a new development! After following @Dusty_Boots instructions in igazor's
link, I was able to play the base game without freezing on quit! Everything worked as normal (in windowed-mode only, not full screen mode) and I could download and actually install items from the store. YAY! Thank you guys for your help!
However, when I tried enabling any EP (only tried up to Late Night), it still froze at quit just as described in my original post. So odd.
I think what I'll try next is to uninstall everything, reinstall, then see if Dusty's instructions work and take it from there.
Thanks so much for the tips, info, and links provided by both of you, @phoebebebe13 and @igazor .