The reason I initially stated that you could use a render engine is due to the fact that you give the impression that you want to take an entire game engine, tear it apart, fix and add to it what you want and put it back together again. Next to the fact that perhaps the things you want to add to an engine might not be feasable or possible in any or proper way (I don't know the source of torque by heart, so I'm not saying anything final here).
With the time and effort you spent on learning how the engine works from top to bottom so you don't break anything, you might as well take a barebone render engine where the graphics part is taken care off and the look and feel is largely free to your own imagining and do everything your way.
I'm not saying this is the best way to go, but also considering the fact that you still need to learn a lot, this might also be a better learning experience for you.
Look at it this way:
I'm not a car mechanic. I know a few bit here and there, but that doesn't make it viable for me to take a car, strip it down, alter/replace what I want and put it back together. Can I do it? Probably, if I take real good care. Will it be exactly what I want it to be? Very unlikely, because I don't know every detail about the car, I don't know if I accidentally removed/altered some dependency which will cause the car to break down (or even start).
Instead, I'd rather get a chasis and slowly build the car up, learning every bit I add. Add it carefully with full knowledge of what I am doing. In the end, I hopefully have what I wanted, but this time, because I took time and care about every piece, I know the car inside out and if something should break, I know where to look and how to fix it.
Perhaps it's something personal, perhaps you simply enjoy the breaking down part. It's all up to you of course.
All I can say is; Take these peoples advice, it's solid.