First thing to note is that the Graylog Marketplace is really a thin front end to Github. Most definitely build up your project(s) in Github with all documentation and when you are ready to present, then add it into Marketplace… because once you add something to Marketplace you can NOT change it.
Marketplace needs some work. I wouldn’t worry about which section you put it in too much, I personally search from the tags. If you are making it one large project then use “Other”. 