Look, you're buying a $125 bike. Other than changing a few things for comfort, I wouldn't bother spending any more money on it to lighten it up except to make sure it has a decent pair of aluminum rims on it. Skinny tires will reduce the road friction and that will help a lot, but if you are commuting, get something sturdy enough to withstand potholes, etc.

I used to commute on folding Specialized tires and those held up pretty well. Stay away from sew-ups. I had a pair and they are a great ride, but I only used them for club racing. They are too fragile for everyday wear and tear. (Forgot to mention, sew-ups take special rims, which are not cheap.)

Lightweight bike components are expensive, especially buying them one piece at a time. Besides, if you add panniers and rack, what's the point?