1994 Lexus ES 300 Is my car getting ready quit for good?

I learned how to drive in November 2008 and brought this car a few weeks later. It has been driving great up till a few months ago. Please bear with me because I don't know anything about cars. First thing is my air conditioner only blows hot air when it is above 90 degrees outside. Below 90 and the a/c blows cold. Second, my front driver and front passenger doors don't open from the outside anymore. One day about a month ago I went to get in my car and I could not open my door. The passenger side front door would not open either. My car doors will lock and unlock with the key, but I have to open the back door and reach around to the front to open the door. The front windows won't go up or down anymore. Only one back window works. To make matters worse, two weeks ago the controls on the drivers door that operates all the windows and locks fell down into the inside of the door. Basically the whole unit that has those controls on it came out of its holder and fell into the door. My car has an all leather interior so, it is hot as hell in the car when it is above 90 degrees and I can't roll the windows down or operate the a/c. WHEW! I live in Indio CA so just imagine how hot it gets. A few months ago I had a new (used) tire put on my car. Since then whenever I drive above 50 mph or up a hill my cars front end and steering wheel shakes, and it feels like my car is struggling. Because of this I can't get on the freeway. Also when I let go of the steering wheel the car starts veering to the right. I have to constantly pull the steering wheel a little to the left all the time. Last night while driving home from work I noticed that my cars heat meter was all the way up. Its always been in the middle. I got scared so I pulled over. I put up my car hood and had no idea what I was looking at. A gentleman drove over and offered to help. I told him about the heat meter. He checked the water and said it was fine but it was not getting to the engine. He told me I could make it home if I turned the heat all the way up until I got home. I think I remember him saying that it might be my thermostat. He said that I could buy the part for around $25 and have someone install it. I am at my wits end. I need my car to get to and from work. Do you think my car can be fixed or has it become a piece of junk? Please help me.