How hilly?

I wore out a chain on my road bike a few weeks ago. It took 2,000 rainy Seattle miles. Mine was a 10-speed chain; if I'd had fewer gears ( in the back ) it would have lasted longer, and cost less to replace. So mine is the worst case scenario for you, and would get you 400 round trips to and from work.

Just wear whatever clothes you're comfortable in, unless you need to climb a mountain on the way in. And get whatever bike fits you and feels natural.

Can you store it indoors at work?