Almost finished with a build of a SSCX bike. Crux 2012 disc with SRAM RED GXP crank with a 42T FSA ring and Surly spacers and 18T cog on the back and a BEER EBB. Brakes are Hylex. Hope to start racing in a week or two around the SF Bay Area (BASP, Superpro etc.)

I built around the Crux instead of a dedicated SS frame since I wanted the flexibility to put a gruppo on it. I was thinking of getting a Ultegra Di2 10spd RD and use remote shifter buttons or I think the hylex levers might have a provision for buttons (I am getting them in a day or two). What else would I need? I obviously need a battery box (or a battery of some sort - I like the idea of putting it in the bars!), switches and cables.

I was thinking of getting a medium cage on the RD and trying a 11-32 cassette. I think in a 1x10 that should be do-able. Happy to switch the 42T ring for something bigger as well. Since I'd have to use a 10spd chain (probably PC1091) I am not even sure my FSA 42T would work since it will be running a 8spd chain.

Is there any clutch options with Di2 RDs? Would I need any chain guards/keepers?