Sorry should have explained that a 50mm lens on a full-frame body will
appear to have a longer focal length on a crop body (1.6x the stated focal length). I say "appear" because in the case of some lenses designed for crop, you can't use them on a full-frame body anyway, so it's a moot point.
But for a walk-around general purpose zoom, you definitely want wider than 35mm. I even feel slightly constrained by 17mm sometimes, and that's when you start the whole process again looking for an ultra-wide angle
IS is amazingly useful, but it won't help with moving subjects in low light, and this is where aperture really helps- bear in mind f2.8 lets in double the light of f4. I'd rather have a sharper lens and large aperture over IS, but it's all down to your intended use.
My general kit is currently the Tamron 17-50 f2.8 (non VC) and the Canon 70-200 f2.8 IS II. I did have a 50mm f1.8 but lost it in the Canal in Venice, I don't miss the 50-70mm range as such, but I do miss the aperture. I've got an M42 mount manual focus 50mm Pentax takumar f1.4 hopefully arriving today which should be fun.