If I accidentally hit a checkpoint or collect a coin, do I have to reset?

A regular coin, no. That's impossible afaik. But a Star Coin or checkpoint, yes, you have to reset.

okay, thanks

it's low%, so you're beating the game with as few collectibles as possible, not just small mario%

What's the rule if you do a low% speedrun at a live event when you hit a checkpoint?

Reset OpieOP

die, enter another level, exit that level, restart the level you hit the checkpoint in