one IFR GPS with nav/com
one nav/com
one autopilot
two Archer wing tip nav antennas (don't use a single antenna with a splitter)
audio panel
Uh, no. Depending upon your local environment:
* One flip/flop comm with standby frequency monitoring works okay for IFR, as I've done for years. And if approach wants you to get weather and you don't have frequency monitoring, you can ask to go off frequency. Second comm is nice, but not necessary. I've had lots more problems with headsets than with radios.
* In 40+ years of instrument flying, I have never even heard of a general aviation plane having two nav antennae. Not once!
* The SL-30 was real cool in that one receiver could give cross bearings from a second VOR while the primary frequency was used for VOR or ILS guidance. These days, the GPS does all that cross bearing kind of stuff but even nicer -- with time and distance to the fix, no slant range correction, nothing. Yes, sometimes the military does jam GPS for practice, but not without warning. You can make your own decision on whether to fly in jamming or not.
* Autopilot is very handy for RVs with their frisky response to bumps, but you should be able to fly without it.
If you look at the history of general aviation avionics, it has historically been the case that pilots were trained to fly with lost capability -- for example, partial panel following suction failure, or no airspeed. With modern avionics, there's lots more capability, and the philosophy has crept in that the avionics should completely protect the pilot from loss of avionics capability. Don't be fooled into thinking that lots of extra gadgets will always provide this protection.
On my last IPC, a CFII "friend" and I did an interesting scenario, simulating loss of the entire electrical system. I turned off the left G3X Touch screen (his screen was still on to monitor engine, etc) and I used the G5 for flight guidance and the handheld aera660 for navigation. Then I shot an instrument approach, hand held. The navigation was sloppy, and it was a pain adjusting power based on throttle position (constant speed prop so no aural cues), but in reality, not all that hard to do. And I've flown coast to coast with a moving map hand held GPS with iPhone for backup.
It's a lot more important to know how to use what you've got than to add more and more stuff. And if you do have a lot of stuff, you should not have to have all of it working to fly -- you should be able to fly with some of it inoperative.
This pontification was written from a US pilot perspective. Your mileage will vary, of course.