That's an interesting setup combining an internal gear with a derailleur set up. I've got a 700c wheel with a 7-speed IG hub but it takes a different type cog/sprocket.

I thought I might be stretching the envelope in the SS/FG section asking about 2-speeds, I'll head to a different sub-forum if I revisit the 7-speed hub use.

I've got some thinking to do, probably end up with three winter projects.