Extreme Creations says "Other required parts are the complete Ducati rear hub assembly including cush drive, brake disc, caliper & caliper bracket. As well as a Ducati 1098 rear wheel or aftermarket wheel to suit a Ducati 1098. A suitable brakeline will also be required."
For my conversions I picked up a complete (eBay) 2007 1098 swingarm with the hub, brake disk, caliper and rear brake master, and resold the bare swingarm. The Ducati rear master is mush so installed a new Brembo rear brake master ($90). I stuck with the 1098 6" wide wheel and lucked in to a forged 1098S Marchesini and an OZ wheel but the cast 1098 wheel works also.
Note there is an very early 2007 1098 axle that is a couple mm smaller than all the later "large" Ducati axles, only matters for the pin size on the sssa lifts.
The rear wheel 55mm axle socket is available, https://www.amazon.com/Wheel-Nut-Socket-Ducati-Multistrada/dp/B09SYRVR7H Torque spec is 208NM!
In my notes I have for compatible 6" rear wheels: 1098, 1098S, 1098R 2007-2009 1198, 1198S, 1198R 2009-2011 Multistrada 2015-2020 also, probably also Multi 2010-2014 the same 6" wheel.
As Jim mentioned the 848 (+ others) wheel will work and keep the 5.5" rim and 180 tire. Not sure if the hub is the same, these may have the "small" Ducati axle but should work with the EC kit.