Maybe too late to add to this discussion, but if you are just going to have one bike to do it all, I would echo getting a touring (road) bike, with wider tires - my Surly Long haul trucker fits up to 42mm tires plus fenders (muidguards) or 45 mm without. That is quite fat, and makes suspension completely unnecessary on a bike you are riding on the road and relatively smooth trails. It gives a much faster commute than a mountain bike or hybrid would, and I have ridden it 200 miles over 2 days with 35mm tires. I also ride it on packed gravel all the time.
For handlebars, you can get wider drop bars, and risers to make them as upright as you want. Most touring bikes are much more upright than a road 'racing' bike. It will be very hard to find a new touring bike in your price range, however, but look for used ones - I forget models, but Surly, Trek, Fuji, and others have popular touring bikes in steel or aluminum that would fit this description.
I would not spend money on disk brakes or suspension for your purposes. Properly adjusted rim brakes should be able to completely lock up your wheels when dry. Disc brakes don't give you more power than that. They will work much better wet, but add costs and complexity. In my case, in the wet pacific northwest, I wish my commuter had disc brakes since 9 months out of the year my rims are wet. I still stop fine, but grinding that grime into my rims constantly makes them harsh, noisy, and wear out fast. For dry weather commuting, I see no point in disc brakes.
