I'm at about the same point in my build ... avionics and engine.
I'm an electrical engineer I and totally believed that the electro-bits would be a piece of cake. On one level, they are easy .. the putting it together is no problem. I have the tools an experience; I've built spacecraft; I have fancy crimpers and strippers and mil-specs, and such.
What surprised me was all the time needed to plan the final package. Unlike the rest of the kit to this point, the avionics/instrument package is not specified in the plans really at all. You need to decide on a vendor (Dynon, Advanced, GRT, Garmin, Steam, Glass, etc), read ALL the documentation, understand ALL the documentation, generate the schematics, engineer the wiring/connectors/cable bundles, switches, power distribution, etc, etc. Only then when the paperwork is done and verified, the "craftsmanship" of routing and crimping can take place, which you might have to learn how to do well, just like riveting (and priming).
It's easily a 150-200 hrs of reading, planning, designing, (redesigning) to get to a design that will work the way you want. It's been fun, but slow!
With that being said, a Dynon fast panel or a big check to SteinAir would help things go faster, but that's only the panel. You'll need to work out routing to the wings, flaps, stick grips, servos, ELT, ACS/strobes, and FF that is completely separate of what fits behind the panel and on the sub-panel.
This is the finish carpentry part of the build. Getting the walls up is quick; the interior takes extra time.
At some point in the future, I hope to put together a set of posts to document my process and what I learned .. these birds teach you lots of good things, some of which are about flying (most of which are about primer ;-)