Camry vibrates when braking

Question

Disclaimer 1
Before I begin explaining my issue, I want you to know that I am definitely planning on taking my car to the mechanic. I just want to know what I am getting myself into so I don't get ripped off.

Discalimer 2
I am a car noob and not a mechanic by any chance. I am a pretty handy person, but definitely not a guy who can just look at a video and be able to figure it out easily.

The car:
I drive a 2007 Toyota Camry Sports Edition. I purchased it used in 2015 April. It had 72,000 miles when I bought it and now it has 137,000.

Car's history:

1. I had a minor wreck back in 2015 when I rear-ended a car in front of me. My front bumper got pushed in to the car a little bit. To the point that, when I finally had the money to change my tires, the guy said he had to push the bumper out a bit because the new tire is thicker than my old worn out one (that was how bad my old tire was!)
2. When I took it to the insurance inspector, he said that (and I am definitely not using the right terms here) "a metal beam thingie that is in the front of the car is bent and needs to be straightened out". I could swear he said "front axle" but my uncle, who is really good at fixing cars (just the old ones), doesn't know what that even means. So maybe I am wrong about it.
3. In late 2016, I drove over a median. The median was one of those short medians, about .5 to 1 foot high. That scraped the bottom of my car.
4. There was a period then where I couldn't afford to get the brake pads changed in time, so I drove around with a pretty much metal brake. That caused the entire caliper assembly to fall out and get stuck in the tire. I had scraped the all-metal on my rotor that it made a deep hole in the rotor! I had the rotors on the front two tires and all 4 brake pads changed then.
5. Continuation on Point 4, the rotor and caliper rubbing each other caused a bunch of metal to get scraped off of either parts and get deposited on my rims. So my rims are practically rusty brown in color now.

Problem:

When I brake, my Camry vibrates a LOT! Like, it doesn't just feel like a normal vibrate. It feels like my front half of the car body is just going to get unscrewed and fly away somewhere. If you have a drink in the car, it will empty the cup for you. It is HORRIBLY bad. This happens more so when I brake from going at around 50 or over. If I am driving 30-35 and brake to 0-5, it doesn't vibrate. But if I come from 50 to even 49, as in, if I brake at all when I am at 50 or over, it does this.

Things I've tried:

1. I read that the rotors get hot and get warped and that will cause the car to vibrate like this. So I bought 2 new rotors and 4 new brake pads, took it over to my uncle's house, and had him teach me how to change the rotors. I changed 1 rotor and 3 brake pads myself. This was no longer than 4-5 months ago. It drove fine for a month, and then it went back to the "a jet taking off" vibration.
2. I thought maybe since I got my 4 tires changed in all different times, my front two tires are better at coming to a halt/slowing down than my back 2 are (I know it sounds crazy, but I am not that smart with cars). So I had all 4 of my tires changed in a one month window.
3. Checked the brake fluid, which scares me a lot. Because, it has been about 2 years since I ever added any brake fluid in this vehicle. But the brake fluid levels were at close to maximum.
4. Checked under the car to see if something is sticking outside/sticking inside/sticking into the tire area of the car. There is a small plastic piece hanging down, but I doubt that piece has the power to shake my car like this.

Questions:

1. Is it normal for the brake fluid to not get used at all over a period of 2 years?
2. The rotors I originally got were the cheapest rotors I could get. Is that a bad choice?
3. Can anyone think of anything that is possibly wrong with this? I am hoping to see any possible issue with my car so I go in with an expectation of what is wrong.
4. If the forums are right about rotors overheating, are there any suggestions for the kind of rotors I can get to reduce the amount of heat the rotor retains? Any rotor brand/style that would actually resolve this issue for me.

Thank you and sorry for the really long post. Just wanted to be complete.

Edit 1
Based on comments, removed some of the unimportant questions so as to be in agreement with the site's standards.

Answer 1

I can give you some help.

The brake hydraulic system is a sealed system that should never leak. This isn't the good 'ol days where you had to top of the master cylinder. In a modern car, you should never have to add fluid. The fluid level will drop as the brake pads wear, but the reservoir is designed to hold enough fluid to take that into account.

So, here is some advice. If you changed the rotors once, and the problem went away for a time, then chances are very good that the old rotors were warped, and the new rotors have also become warped. This can and does happen from overheated rotors. From your descriptions of everything that has happened, I would:

Get an alignment. They will normally inspect the car enough to find any suspension issues when they do this (because bad suspension means they can't align it right, and the customer will be mad). Poor alignment can lead to uneven braking, but this is really just a general recommendation because of the accident and the median.

Replace or rebuild your brake calipers. That whole metal-on-metal braking is hard on all the parts. Metal shavings getting into crevices, parts heating unevenly and heating too much, the pistons over extending, etc. A caliper that doesn't work smoothly and doesn't retract properly causes the pads to drag and... overheats the rotors.

Change your brake fluid. Over the life of the car, it does absorb moisture, and it can be damaged by heat. Replacing fluid is a part of the normal maintenance schedule. Ideally, do this at the same time you replace your calipers. Bad fluid can cause corrosion inside calipers in the worst case.

As far as buying the cheapest brake rotors... Best bet would be to get recommendations from the owner forums. Also, price OEM parts. Sometimes they are way to expensive, but on some parts, it's not a huge difference.

Answer 2

also when torquing the wheel lug nuts,if they are not evenly torqued, over time it can cause rotors to slowly warp. I bought a big torque wrench so i am sure mine are all even. Also very possible if a shop does it there air guns could be off and not apply even torque too all lug nuts,regardless of what they tell you.