I like to have main things on the internal drive as I like to have peripherals plugged in as little as possible on my laptop. The other reason that I like to have most things on the internal drive is that time machine only backs up the internal drive (AFAIK). I do make drag and drop backups of music and photos onto external drives too just for belt and braces, although maybe not as often as I should.
Tbh I don't understand NAS and stuff like that, too complex for me
Oh hell no, I'd have far too much garbage if I did
TBH when I get the new system I'm going to go through a bit of a culling process and I'm hoping to at least half the photos. I won't get rid of Holiday and family pics obviously, but outside of that if I'm being brutally honest I'm probably only happy with about a dozen of my photos if that.