My ideal minimal panel would be the traditional guages with the
addition of an electric AI for backup. I would not have a backup vacuum
system. But I would want batteries in the AI. This way I have two AI's
each running off it's own power source.
I would have two VOR/GS, an IFR GPS and an all electric autopilot
coupled to the VOR/GS with just altitude hold. I would have a handheld
GPS and a handheld radio, with rechargable batteries plugable into the
aircraft power supply. I would also have some battery operated cockpit
lighting, permanently installed.

Not included would be DME, ADF, or Marker Beacons, nor an HSI (with an
autopilot and an IFR GPS, you don't really gain much with an HSI).

If I went with onboard weather, it would be one of those systems that
downloads from the satellite radio the graphic weather to a display.

Don't forget that money issues aside, all this stuff breaks and it
takes the airplane down while it's being fixed. So keep it as simple as
possible, though the above system is not that simple.

I have traditional gyros in my plane, an all electric autopilot
coupled, a VOR/GS and an IFR GPS. As it is, I usually have to repair at
least one item every year. My IFR GPS just got back from King, works
great now! But my autopilot still isn't working. Autopilots are great,
but are known for unreliability and frequent expensive repair. There is
a good argument for just a wing leveler. Safetywise, in IFR that is all
you need. All the coupling is just convenience. But it needs to be all
electic.