Sourcing Ultegra 6800 hydraulic disc is not as easy as you think. There are a few websites that let you mix and match the components.
Texas CycleSport had a good site but mostly it was the phone calls and emails that worked for me. They assured me their Wheels Mfg. bottom bracket they supplied with the groupo would fit fine. I got the compact crank at 175mm, the medium cage derailleur to match the 11-32 cassette and hydraulic/11 speed levers and calipers.
There seems to be a dizzying array of headset specifications. In the end, mine seemed simple enough. I needed "IS 42/52". WTF is that? I ended up calling Cane Creek and got the low down. My frame has the bearing races already pressed in the frame. All I really needed was the bearings and no special tools to install. Cane Creek and Campy offer bearings for my threadless tapered integrated headset. I ended up going with Cane Creek 110.