I have a D-100 installed in an RV-9A. I installed the unit during the aircraft build and it wasn't hard to do - you just need to be confident at either soldering or crimping wires into D-sub connectors. The biggest pain on a retro-fit is likely to be routing all the wires around the aircraft. The most fantastic thing for me is getting a DI/Compass that doesn't need adjusting all the time and points where it's supposed to. We've managed to swing the compass sensor on our Dynon to within degree.
If you have the panel space think about fitting 2 separate screens for EFIS and EMS. I like to fly my D-100 with the DI showing - and I don't know how that would work with the engine data also on screen.
If you can do it easily then the Dynon AOA is worth installing - but it may be too much trouble on a retro-fit. It requires fitting the Dynon AOA pitot head and an additional pressure line to the Pitot.
Dave