Agreed on the battle promo usage for the Battle of the Bits Instagram; one thing that I've seen from most creator Instagrams is that they usually promote and generally tease stuff that's coming up (e.g. a new video on their YouTube channel), so it'll definitely be great for promotional purposes and related engagement.
For the yuttubs, if the content were exclusively going to be music, I'd say maybe 2 or 3 videos a day could suffice. There are over 20,000 entries if the number in the entry URL is to be of any consideration, so you wouldn't have to worry too much about running out of material to transplant. Of course, if you're also going to throw other material to the channel like full-fledged teaser videos for major battles, then maybe the frequency could be relaxed a little (maybe 1 or 2 a day), but those are just my thoughts on the matter.
All that said, I should subscribe and follow :o