Quick question: should catchup be on or off in arcade mode? I've been running without it but am not sure if i should. Are there any rules about this?

I'm unsure. Catchup usually just makes the people further away from 1st slightly faster so shouldn't have much affect on gameplay.

As far as we know it doesn't matter if you have it on or not because it only affects the NPCs. So I think you can freely choose the way you want to do it.

Having catchup off may make it slightly easier since the NPCs will likely be further away so pickups won't be so much of a worry.

I mean, yeah, but if you ever really played the game you'll know they barely shoot you anyways. It's probably actually better for them to be close to you so you don't have to lap them and they won't drop a random tornado.

So yeah, it really doesn't matter too much, do whatever you prefer.