American Mcgee's alice

I am interested in potentially trying my hand at porting this game to Vita. It is based on ID Tech 3 which is already technically playable on Vita via Quake 3. My question is where do I even start to attempt to do this? I have some knowledge of Python and c but I am not even sure where I'd start porting the code. There isn't an open-source engine I could port so do I use the original engine and try to port that? I am just a little unsure of how I would start this project.