What is the best 'look' to a speedrun stream? Would it be fine to have chat and a facecam over the minecraft footage, would that risk not being a legitimate run?

As long as the actual Speedrun is visible is fine (not covering hotbar or a Big part of the game i guess) Voice, sound, music, even timer are not necessary

Audio, music, timer, etc. are all optional. All we need is to be able to see what you're doing ingame clearly.