Key thing for me is getting a bunch of people who are doing specific raids often enough to get familiar with the tricks - I see improvements every time we go through BWD, even though it's not the exact same players every time.
Minimum nights a week - is it the nature of having a guild full of "mature" folks, people will necessarily be on-and-off. I like to do raids whenever I can, but don't necessarily know how frequent that will be. If that makes me "casual", I am cool with that!
The efforts to organise raiding are observed and appreciated, by the way. I organised a CS clan for a long time, and I wouldn't underestimate the challenges of getting 10 spods online and ready at the same time!