RE: rc hydraulic system?
Unless you're only going to be using the car for show, it would be a complete waste of time and effort in my opinion.
There is no way to make the electronics control a hydraulic system that would be allow the car to drive normally.
The spring and oil shocks will not work without some out of the world pinching system.
I'm not sure how air shocks work, but I'm sure it would end up the same.
But if you decide to go for it, good luck!