I think that 36 videos on a playlist is pretty much on the low side.
But I don't necessarily think that 100+ is optimal either.
Somewhere in between, with people watching each others videos, would be nice.
I am not good at commenting, since I often have to listen while doing things on the side, due to limited time.
But I usually listen to pretty muach all the entries, while still noticing the the number of views for most videos as often way lower than the number of seasonistas participating.
I don't know if you can trust Youtubes viewcount though. For one song that I spend all week practicing, youtube says that it got 5 views. Average viewing time 36 seconds. It was 1.43 long. So those few people who actually clicked it, in average listened to 1/3 of it. Total playing time 3 minutes. That is the same length as one of those dozens of songs that I listened to that week.
Some themes might be harder for some people than others. So you cant expect an the same number each week.
If a theme is too broad, it actually doesn't inspire me. Some kind of restrictions demands creativity.
It is just easier for me when the theme is about the lyrics or theme of the song, rather than the artist, since it is always hard to learn a song by a new artist you never heard of.