First, read the manual. Adjusting a deraillur is not rocket science. I believe all you need a a #2 Phillips and about 10 minutes.
Trash the seat, or accept it is a short distance bike only. For my wife's $130 Schwinn mountain bike, we bought the Bell gel seat at Wal*Mart. Does the trick; is much better than the stocker.
If this is anything like the aluminum Kent I bought a couple years ago, the rear shock absorbs about 50% of your pedaling energy. If that is the case with your bike, consider defeating it, or replacing it with a solid bar of something.
Also, the seatpost on my Kent wouldn't go high enough to let me get good leverage on the pedals. It was a standard diameter seatpost.
It was an expensive lesson, but one I learned. There is a reason why the better makes cost more. They actually put some thought into design, aside from bottom line price.
Good luck, and don't let this discourage you from folders altogether.