I desperately need some help in determining what kind of bike would best suit my needs, and which specific brands/models I should be looking at. Here is a rough description of my requirements and preferences. I know very little about bikes, so please go easy!

Essentially, I want a bike that is light, fast, and durable. I will ride primarily on the road/sidewalk, but I do enjoy the occasional dirt/light gravel trail. I will be riding in a variety of environments, but 'urban' would probably describe it best. I always ride in the highest gear and, as a result, find that I constantly encounter the same problems. More specifically, I continually have issues with the following:
- Chain stretching/skipping
- Drive train wear (teeth wear out)
- Chain popping off

I prefer:
- Racing inspired look
- Low profile, straight handlebars
- Durable, racing-like tires
- No disc breaks
- High gear, light as a feather

Given my 'riding style' and preferences, I think a single-speed, hybrid bike would be best. I was tentatively looking at the Trek Soho S, with puncture resistant tires, but I don't know if there is a better alternative. Would this be a suitable bike for me?

If so, what is the difference between the Trek Soho S and the Trek District, aside from the carbon belt? Would it be possible to upgrade the Soho S with a carbon belt at a later date? I love the District, but it's just too expensive at the moment.

Thanks for any/all advice!