Ouch! Sounds like you have a few issues here. If we just focus on the trackpad I would replace it, sadly it’s part of the uppercase assembly Upper Case assembly. You might find a junker which you can salvage the Trackpad. But from your description I fear you have a bit more broken here.
The case plastic becomes brittle with age. I often find visible cracks in the case and the stand-offs are often sheared off from the impact.
It maybe better to look at finding a newer used system before going deep in the expenditure this system will likely need.
I faced a similar issue a few years ago, I had two 17” MacBook Pro’s. I cried when my last one died! It was so useful when I was on a shoot with its massive display. Sadly the GPUs just didn’t hold up due to poor design and manufacturing and Apple dropped the larger sized system. The 16” is their try to get us back, too little and too late😟