There are plenty of virtues to having variety in your match setup. It adds some variety, some chances for narrative, and also forces players to adapt to different strategies. However I also see it as perhaps almost too varied, especially given the potential contestant turnout. I think just going with a straight up 1v1 bracket (with the exception of the last match) throughout the whole tournament would feel more consistent and structured than throwing in team fights and 4 way battles.
That being said, all that can be tried out at a later date. For now this is how you laid out your tourney and I'd rather you stick to that first. Who knows? This might work out perfectly fine and I'm absolutely okay with that.