Don't overthink it. Start out with a basic, utilitarian bicycle. After you ride that for a few months to a year, you'll be in a much better position to decide what is really important to you.

I've been riding a $300 hybrid bike for 24000 miles and 6 years now. It's still my only bike. I change accessories based on season; lights and tires mainly.

Don't spend a ton of money on anything right now, but on the other hand, don't buy junk. I have more crappy lights than I care to think about, and I've spent more on junky lights than I eventually spent to get good ones. Same is true of some other accessories.

You can commute on anything, but you do want a bike to be, at minimum, safe. A used bike is great for this and springtime is a prime garage sale season. If you can find a bike that is in decent shape, great. The tires will probably be dead, but if you can pick up a good basic bike for $50, spend another $50 at a bike shop having them put new tires and tubes and brake pads on and giving it a basic once-over for you, you'll have a pretty good bike for cheap.

Watch out for wally-world bikes. The easiest way to tell if a bike is junk is to look at the brakes (the part of them that's at the wheel, not the grip levers). If they're made out of stamped sheet metal, the whole bike is probably junk. Similarly I'd personally stay away from a bike with steel rims instead of aluminum. Steel is a lousy surface for brakes to act against, and a bike with steel rims is probably really old. Old isn't necessarily bad, but an old bike at a garage sale has probably had spiders living in the gears for 20 years.