1. Make sure the 19'' bike would fit you. At 5'9'' it might be a bit big.
2. I think it would be worth getting the bike if you used it for a year without putting any other money into it. Save up some dough for a new bike, while spending some time riding this bike. See what you like to do and don't like to do while riding.
3. see if he will take $80
4. Do not upgrade it.