Congratulations, you're on your way to getting something that works well for you and a lot of us commuters. There are a lot of us riding 90's steel diamond framed mountain bikes with thinner tires, they make great commuting bikes. Narrower tubes will make putting the narrower tires on much easily, and trigger shifters make shifting your newly cleaned chain even easier.

Now that you've wandered into the long running discussion of which frame material is best, you can look forward to some similar enlightenment if you ask if you should wear a helmet, wear cotton, wear underwear, wear hi vis clothing and ask which light should I use....