Due to stupid weird feet + PF, I have loads of Fitflops: rally trainers (limited edition design ones, not the plain colours), mary janes, flip flops, various boots...
But you do have to pick carefully as some of their designs are ghastly. Plus the footbed designs vary. I now know (expensively!) which ones are no good for me!
To your questions:
The mary janes are surprisingly delicate for FF. The thinnest sole they have I think. I can still wear them all day though I do chuck a gel heel cushion in if walking on city streets or similar hard surfaces for a long time. General driving and office is fine without
Boots: This is where the footbed issue really comes in. I have one pair (now sadly falling apart) that suit my feet, and 3 or even 4 pairs that have a different sole that do not. They seem obsessed with making gigantic boots for some reason.
Rally trainers: the base structure is super comfy, but they do look a bit like you are going to lawn bowls or the darby and joan club unless you get a funky pattern or design, usually limited editions.
Flip flops: I live in these in the summer, indoors and outdoors. Come in fantastic colours too. They are quite stiff new, but break in very quickly.
I never pay full price unless I really like them (like the leopard print mary janes which went in my basket about 30 seconds after I got the email!), and I get most of them off ebay new, just cheaper.