Congrats on your purchase.
I've the GSW690III but I think they are the same camera for the most part.
Filter size should be 67mm. Domke f3-x is what I use for a bag, and its the perfect fit, function, and look. Any Strap will do. However, I go strap less, If I'm not shooting it goes back in F3X. I only have strap on fast shooting cameras like my F3 and F4 Nikons.