1. The door is probably the hinges either loose or not fixed properly, you have enough ventilation with the remaining
windows
2. The tongue looks to have been poorly extended
3. It is possible to reinstall the
furnace, cost is variable depending on what they did.
4. It looks like amateur body work and
paint job. It is hard to say unless you see it.
Sometimes it is better to buy something that has not been "fixed" than to try to fix up someone elses work.