Congrats on your decision to give bike commuting a go!

I have a co-worker who rides a GMC Denali maybe 2 days a week, 35 miles round trip, and he has had pretty good luck with it. He is running into some trouble with it now, as can be expected from an entry level department store bike, but he's gotten almost 2 years of service from it, and has saved enough money to buy a better bike. It is a good starter bike.
If you want to use a rear rack, you will have to use P-clips or an aftermarket seat binder with rack mounts.

Is your route hilly? flat? do you encounter frequent rain and or snow?