harmonic balancer- Unless there was a chunk missing out of it or it was bent somehow, somebody ripped you off. It probably didn’t need to be replaced.
accessory belt- Sounds like someone took the alt. out and when they put it back in, they used the wrong bolt.
idle- your throttle body runs better once the coolant running through heats it up a little. Could be a bad seal or you might be able to adjust it with the idle control screw.
oil pressure- what are you monitoring it with? stock gauge? that could be the problem. I know the gauge on my 2G acted weird sometimes. Thats thinking optimistically though.
Compression test might be able to reveal more.
Brakes- Are you losing fluid or do the brakes feel spongy?? If your losing fluid, go find a dry parking lot and pump your brakes while at a stop. Get out and look for fluid on the ground.