I'm not saying players will control all of these, I'm saying typically you'll be fielded in a larger force of NPCs. As I'm unsure how small squad based missions work for Sisters.
It's novel material, and I'm sure you're already sick of me basing my arguments on H&A, but in the last stretch, they're basically a single squad with... five sisters plus retributor I think on an infiltration mission. So I'd say depending on the mission, everything from large to small scale goes.
Ahh ok, I meant to read those books before getting this RP going but... That didn't happen. It sounds to me like this is going to work much like a Deathwatch RP.
If I may make a proposal? Just have us forming up a squad that's apart of the same large battle as the main sisters force we just have our own task. Since we have a few particularly inept/crippled sisters perhaps first mission is trying to prove ourselves. Our Order is attacking a large hub of cultist holed up in a factory district and we're being sent to cleanse and purge one of em on our own?
Well I am more in for we are all in that huge battle but we just work together closely as 1 squad. Imagine a Space Marine RP where an entire company of 100 men fight and we are simply 10 of those.