Is multiplayer allowed for this game? Item management can be done by people when it isn't their turn, and more brains can help newbies like me (and my friends) with remembering the route (or even having P2 and P3 reading the route while P1 is driving). I suspect it's a little slower, because you have to take time setting up who controls whom, and I don't think there's any multiplayer tech that speeds up part of the game, so I think it would just be a crutch to newer players.

While I will say being able to pay attention to your notes and running the game without someone reading to you is just a skill that speedrunning in general will demand, don't sell yourself short in that regard, there is no reason to not allow such a thing, so go right ahead.

As far as using the built in co-op, it doesn't allow any inherent advantage over someone playing the game by themselves so I see no reason not to allow it, however coordinating between 3 people is likely going to only be a hindrance given how turns in this game work that I also wouldn't recommend it unless you're just kinda wanting to do this to mess around with some friends and not planning to shoot for more optimized times.