You made so difficult choice for a newcomer: you want to start your TASing hobby with a 3D shooter game. Every shooter for N64 should be a tool-assisted speedrun, i.e. aims for the fastest time. Project 64 is not accepted on TASVideos, so you should download Bizhawk emulator! Unfortunately, there is no so much emulators for different suggestions, Mupen 64 has bad emulation and very few TAS tools.
To start with, you should read everything in Movie Making spoiler
there to know the basic knowledge about TAS making. Remember, only high-quality movie have chance to get published on TASVideos.org. Every movie must be done frame-by-frame which takes much time, not some days fastly in slow motion!
I didn't find Battle Tanx entertaining for TASing. I had a movie with a short WIP, but deleted.
Good luck!