I probably would never recommend 100 gems because in mose scenarios treasure gets hosted with a 100 gem max. And unless you're planning to play treasure by yourself, 100 gems isn't gonna be enough.

I would say add between 180 to 210 gems, depending on how many people will be playing in the level. As I've seen from hosting Agama's "Cursed Treasure" levels, they barely have enough gems for online play. The default treasure level on jj2 uses about 210 gems, so you can use that level for guidelines.