Biggest issue is removal and re-install of the bottom bracket, which is likely a press-fit, thus might need the services of an LBS. You need to do this in order to lay in the E-Tube cables and find a place for the B port. Chasing the cables isn't difficult after the b-bracket is out and I'm assuming the frame uses internal cabling for the mechanical system currently, thus should have the holes sized for the E-Tube connector. OR the frame has one of those nifty removable access hatches on the bottom of the b-bracket that allows easier access to the cables thru this area. My Specialized Chisel mt. bike has one of these. If doing all this yourself, you need the tools and skills to install a hydraulic brake system as well, such as connecting hoses and feeding fluid. If your h-bar and stem are setup, you can use the bar-end A junction.

I got my system from Texas Cyclesport as they package and price well. You do not need a new crank, might want to put in a new b-bracket while the old one is out, do not need the brakes or rotors, so need to price a system of;
- Di2 hydro shifters
- Di2 F & R derailers.
- Battery and a seat tube holder
- A junction
- B junction
- BT unit if you want to configure using BT or want a BT connection to a cycling computer
- 6 or 7 assorted E-Tube cables

Kit for above from Texas is $1169