An IFR Searey! Got to be cool. Rotax? Ducatti volage regulator? All your volts go through that VR. A VR on the cutting edge of motorcycle technology.
I would go with the optional backup battery for the D-180. I would suggest the back up ASI & Alt. I would even go with a turn coord with a venturi tube. The D-180 can be configured with an EHSI and that should deal with your dislike for the old style OBS/CDI. The D-180 can also take inputs for VHF nav with glideslope and that covers all bases. Iff you go with GPS only, remember check RAIM before TO.
The venturi can also serve as an emergency bow mooring cleat. I like B.U. steam gauges. I had 1K hours in a glass cockpit and still used the steam gauges during t.o. and landing. Your results may be different. Good luck.