Speaking as someone who's been involved in the professional publishing world for over ten years, I think Bass Player magazine has a good format -- artist profiles (big and small), gear reviews, CD and DVD recommendations, transcriptions, woodshed stuff, luthier articles (both "how to" and builder profiles), and a small sliver of community content.
I think the one thing a gospel music mag must have that others don't is a real examination of the artists' place in the Christian culture -- their attitude toward worship, how their faith influences their approach to playing and business, and how they handle the lack of a set format within the gospel music industry. The magazine could also generate a lot of material by examining the varied styles of gospel music -- quartet, contemporary, urban, rock, hymns, etc. Maybe even switch the styles between the different departments each month so it has something for everybody.
My one concern is whether the gospel bass market by itself is large enough to support an entire magazine. I'm not trying to be discouraging, because I would definitely subscribe, but I'd want you to get a large enough audience to keep you going without forcing you to compromise your initial vision.
