Yes to avionics master
Boy you guys take the fun out of it. Good posts I agree 100%. In fact my ICOM A200 says "DO NOT turn ON power until the engine has been started."
Plus convince as said
Avoiding single switch failure point can be done with two switches in parallel, Or as Bob shows a second switch (emergency) E-feed direct to battery with anti back-feed diode, makes it a winner.
99 out of 100 avionics shops recommend an avionics master.
As far as single point failures Bob N., God Bless him, but he does go crazy with it. You could go with just a double pole single throw switch in parallel. It is like two separate switches. Granted you are going thru the master relay but how often does that happen. (Every RV has many single point failure points, one prop, one crank shaft, one left/right wing spar, one brain between our ears. How many buss'es does a single engine plane need? "Yea, he crashed, the prop fell off and the wing followed shortly, but his avionics are still working.
)
I mean he is right, and its better to have two switches and a second path direct to the battery (E-buss), not thru the master relay.
However for a day VFR only no fancy avionics or EFIS its way overkill.
Really
switches are very reliable. If you get an high end Mil spec toggle its going to last the life of the plane. Once you "MAKE" the contact its not likely going to die suddenly, I think. Switch damage is done on the make/break throw. Once you're hooked up, you're good to go. However I do have the E-bus concept. Why not? With electronic engine and flight instruments it's warranted.
George