Having multiple problems

1. I have to pump the gas to get it to go at all times. And it barely makes it up hill. It has no power and I can rarely get it to go over 25 miles per hour. I was told its not the fuel pump, as it would not run or idle like it does if it were, I am goin to get the fuel pressure checked. And have been told its probably the fuel pressure regulator. But have also been told it was the catalytic converter, so I spent 250 to change that and the bad muffler, then I was told it was the spark plugs, then was told it was the fuel filter, so I spent 70 dollars on getting those fixed. Ive also been told it could be the cap and rotor, I got the rotor changed but the parts store didnt put the cap in with the rest of my parts, so I have to rebuy one. Im at a loss with this car, ive put more into it than I paid for it, but cant afford a different car. So im wondering, what could it be? And when I have the fuel pressure checked what are the things that could be causing fuel pressure problems other than the regulator and how do I know what it is? I dont want to spend 65 dollars on a regulator and that not be the problem.
2. My heater only works when im driving, or when its been sitting and idling for over 15 minutes. I read to check the coolant, and my coolant level is fine, so what could be causing that?
3. My sliding door gets stuck and I have to wiggle it back and forth to get it to open and sometimes I have to crawl in through the front and kick it open. Im assuming it is the latch on the inside that is getting stuck, how hard/expensive is it to replace the latch? I have sprayed it with WD-40 and that didnt help at all. If its not the latch what else could be causing it to get stuck?
4. There is also a strong gas smell when idling or wehn I shut it off, I know there is a manifold leak, could that be causing the strong smell? Or could something else be causing it?
5. Do u have any tips on any of my questions, or any tips on other common problems with this particular vehicle?