I also agree with the more challenging but less frequent battles for various reasons. One, I feel like it will set the pace pretty well for the game, it would make sense, and two, I'm sure you could use it to your advantage by setting up the encounters, adding some flair to them, etc.
A big plus is that you'd be able to more or less set the balancing for the game to your liking and it'd be easy to tune. Given you're not relying on a factor like players grinding and stuff.