In future you can ask at the
Newbie Corner, or on
N64 Emulators page for questions like these, since topics on this forum are generally reserved for discussion points for specific games.
But to save your work, just simply go to Movie->Stop Moving Recording. That will stop the movie on the current frame, saving it for later. Obviously just 'play movie' to see what you've done up to this point. To continue recording your TAS, play the movie, but do NOT load it as 'read only' mode; otherwise, it'll be for viewing purposes only. Loading a savestate while in 'read only' will simply skip ahead to that point and continue playing the TAS, but if it's not 'read only' mode, then loading a save state will allow you to continue working from that particular point.
And for TASing OoT, good luck. There's an ongoing discussion in the
forum about what would even constitute 100%, let alone coming up with a decent route.