I generally hate the strap that came with my 501. It gets in the way of the winding knob and the dark slide. But I'm too much of a klutz to take it off and trust my reflexes to not drop the thing. So it's still on, with much cursing on my part.
Filters are pretty easy to find and KEH is probably the best. Don't want to take a risk on scratched/bad filter over the stunning Zeiss glass. Also speaking of glass, I have a 60mm on my 501 99% of the time. Love that lens! And I don't generally like wide lenses but this one is a perfect happy medium for me.
And I do a lot of fast hand held shooting with no issues. But I also know my limit as to when my shaky hands will give out and when to trust a tripod.
Go for it! It's a gem of a camera and every time I look through that baby I always say to myself "the world just looks so much better through a hasselblad!"