16 miles in one hour is a pretty fast pace. If you are measuring your speed using a cyclocomputer, I would calibrate it. Map out a 1-mile course on MapMyRide, do that course, see how close your cyclocomputer matches up with it, and adjust your cyclocomputer's wheel diameter settings accordingly.

Seat comfort is a highly personal thing-- Everybody has a different butt. If you can't get comfortable on that seat after a few rides, you need to find a new saddle that is comfortable to you.

BTW that 7-speed freewheel on your bike might become troublesome later on. An upgrade to a more reliable freehub/cassette system might be in your future.