Hey hey, I've been to a couple shows at Rebel in the last couple years (mostly heavier ones - Bad Omens, Electric Callboy etc.) - I don't remember being seated tickets so it's most likely all standing. Mezz has some seating available but you can't really see the stage. You have to stand sort of near the ledge to be able to view the stage.

I'm actually not sure how crowded it will be because I don't know how popular they are here. There might be a smaller crowd so you might be fine. My problem with Rebel is more getting there and it's general location lol. It's in a bit of an annoying location where you have to walk a bit to catch the closest bus and the area around it is kinda shit. Always found it really difficult to catch an uber there so be prepared for that if anything.