I think that a vintage touring bike or older CX bike would suit your needs well. You can find some really great ones for about $450 on down. I have paid more like half to a quarter of that for my bikes. Even a good older mountain bike with city tires might be good if that is the way you want to go. Most bikes of these types will have room for wider tires, fenders, and braze-ons for racks and fenders. I think that you can easily put together a great bike to meet your needs for about half your budget. But then, you may have to learn a few things along the way. If you are willing to do that and like that kind of thing go that way. Otherwise, for an easier switch, just go with a newer used bike - possibly the hybrid type. I prefer drop bars, although I have trekking bars on the one hybrid bike I own. Both work well for commuting and in my opinion, are better than straight bars. You get more hand positions.

To find the size you need, I would check out this article. If you measure your inseam correctly and find a bike with a stand over height within a cm or two you can always fiddle with an appropriate length stem and seat adjustment.

You may want to look around on the C&V forum and the touring forum for some ideas.