I think a lot of what you need to think about is not so much BIKE-related, but related to the fact that you're going to arrive sweaty. I don't know what kind of job you have, so that could be more or less of an issue.

Considerations for the bike:

• Get something with gears, esp. low gears for the hills. You've likely forgotten how hard hills are on a bike since you were a kid, and they're harder now that you're likely heavier and a bit out of shape
• Get something that rolls smoothly on pavement; nothing with knobbies
• Get something that will take a rack & fenders. It's SO nice to carry luggage on the bike rather than your back. (sweaty)
• If you can afford an eBike, get one. Something of decent quality that is pedalable too. (I like Aventon) You'll thank yourself on every uphill or headwind. This will also remove a lot of the sweat-related concerns below.

Considerations for the commute:

• Bring spare underwear and baby wipes or Quick Dude Shower; there's nothing worse than being swampy all day.
• Have a spare shirt at work
• Water bottle (one should do, for this commute)
• Sunscreen for the ride home (keep at work)
• Put FlatOut in your tires, unless they're really skinny
• If you don't have luggage at first, try a messenger bag with the anti-rotation strap. You can wear it lower on your back and it won't be as sweaty as a backpack.
• Get lights for your bike, esp. a bright flashing rear one. You don't want to hear the ol' SMIDSY. (Sorry mate, I didn't see you) Planet Bike