John,
Carl;
first off I greatly appreciate your response. People with your experience are what I am looking for to decide what to do for an electrical system.
I haven't made my mind up yet except for one part, and that is only one battery. It will be 1 size bigger than I need, so my "backup battery" will be built into the main battery. To my mind, the battery is the most reliable part of the electrical system, I don't see the requirement for 2. I do see the requirement for more capacity, if the alternator fails. I will replace it every 2 or 3 years, and check, and clean, the contacts religiously. Especially the ground.
The aviation and automotive world went after reliability differently. Aviation assumed some parts would fail, and designed backups and multiple load paths so the overall system would fail "softly". Two of the terms used are "Fail-operational" and "Fail-passive". 50 years ago, that was not just a smart choice, but required. Electronics were unreliable, gyros,magnetos were and are still, unreliable, everything was unreliable. The dispatch reliability of the best airliners is over 99%. They have so many backups, and associated wiring, that little things break all the time.
The automotive world is different, because if your car stops, you pull over and try to fix it. They went for no backups, but over the decades made every part as perfect as they could. In the end, even though a Honda Accord is 100X as complicated as a Model T, the Accord is 100X or more reliable, because every part is darn near perfect, and doesn't fail or wear out for 10+ years. What is the dispatch reliability of a Honda Accord or Toyota Corolla? If it were 99%, you would trade it in for a better car. It is as close to 100% as you can get. For the first 10 years, usually the only time it won't start and run is if you ran down the battery, or didn't replace it like you should have and it died after 7 or 8 years.
I have been reading about electrical systems on small aircraft, and they seem to me to be relics of the past. On a certified 1958 Cessna 185 or Bonanza, they probably still need to be. They assume that a lot will fail. Building a homebuilt in 2017, I believe very little will fail if done properly, and simply. Technology has made a lot of what we need better, and for us, simpler. I might want to have a backup for the least reliable component. In my experience, which is not light aircraft, that part is the VR. My experience with external VR's in the marine world, I only saw a couple fail, but a couple of them, did fail. Internal VR failures in the automotive world, I have seed dozens. I have seen a few alternators in really bad shape mechanically, but they were all still charging.
I am going for the Honda Accord model for reliability, but the experienced pilot in me wants a little redundancy.
So I haven't decided yet, and don't have to. I will be looking into it, mostly from people like yourself with experience in this part of the aviation world. I will try to select the most reliable components I can find, and install them with great care. Thanks to forums like this, it is easier now than ever before.
Thanks again Carl, and for anyone else that chimes in.