Q: should I replace this alternator or get another car?? I am a senior citizen without a lot of money

Your problems do not sound related to the alternator specifically. I would not replace it unless it has been checked and confirmed to be a problem. With the number of issues you are listing, your money may be better spent in having something along the lines of a used car inspection. Whether you have it done at a local repair shop or make arrangements with a mobile technician, for a flat fee, they can inspect the vehicle and give you an idea of what is wrong with it, I would do something along those lines before I would spend money to replace a part that has not been confirmed to be the cause of any of your issues.