As for the tires, I started commuting on an old mountain bike with Continental Towne and Country 26 x 1.9 tires. After maybe 300 miles, I thought about a smaller tire, and not knowing if I would like it, I went with the Forte 26 x 1.5 tires (9 bucks a piece). Looking at the specs, the smaller tires were each half a pound lighter than the larger ones, and it made for a better ride and I could actually notice the weight difference. I'm not big on the bike weight, but if you are looking at it, wheels are the first place to start.
My commute is 24 miles round trip and I will stick with the 1.5 inch tires. It may ride a little stiffer at 50psi vs the 40psi I was running in the continentals, but for a mid range commute, it works better.