Alternator or something else?

I love this car! I’ve been driving it for 7 years with no trouble. 2001 with only 79k miles on it. I take great care of it. I changed the alternator 3 years ago. Gone through a couple batteries. Replaced all 4 tires last year along with front brakes. Had some engine work done in May because when it heated up outside and was time to turn on the a/c… it started making a humming noise and if i came to a complete stop and didn’t turn off the a/c fast enough… it would die. It didn’t do it all the time, but enough to make me crazy! so of course when i brought it to the mechanic, it didn’t act up on him. I explained the problem and he thought it could be a sensor of some sort so he took a chance and replaced it, also welded new engine mounts (which stopped the rattle I was hearing/feeling). He couldn’t find anything else wrong and it hasn’t acted up again until last week. It died on me and after bringing it to NTB, they found the battery was fine but the alternator was out. AGAIN. plus there are no working back brakes and brake fluid is leaking. AND, the weird humming noise is back. It stops when I turn off the a/c. They want $1000 to fix it up again, but they don’t know what the humming is coming from. my husband is looking at getting a newer used car now and using the $1000 as part of down payment, but we JUST got 100% out of debt and have been putting money in savings for the first time. We have 2 kids to transport between school and sports so I understand the need for a “safe” vehicle. I really REALLY don’t want to cut back on savings for a car payment! So i guess my question is: what is the humming? is it common for a 9 year old car to need a new alernator every few years? is there something else I should have them check? should i suck it up and get something else?

here is a list of minor/annoying things that are wrong with my precious car: are these signs of bigger problems? NO LAUGHING ALLOWED:

auto light switch stopped working, so have to manually turn lights on and off.

lighter shorted out (replaced fuse and blew again in 3 days) so can’t charge my phone.

remote entry stopped responding, bummer

every once in a great while, if i’m driving at night (rare) the headlights and dash lights flicker and have gone out for a few seconds (SCARY)

power windows move up and down slow, or not at all.

poor car =(