Sunfish,
You have me really puzzled, why is WAAS plus GPS needed for the above, as I asked, do you anticipate Cat. 1 or lower precision approaches??
You don't need WAAS for ADS-B. Why is WAAS going to make any difference to the GPS coupled to your autopilot??
As for the last paragraph of your last post, I do earnestly suggest you acquaint yourself with the characteristics of GPS III, which does everything that "legacy" GPS plus SBAS/WAAS does, and much more. And more reliably.
As I have tried to get across to you, I have been in the farming and mining business for most of a lifetime, longer than aviation, I really do know what is possible RFN, and I am looking forwards to the major benefit to most of us, saving some fees, and perhaps a small increase in accuracy, compared to what we have now. But for most of us, 1-2 cm versus 2-3 cm is not going to make a lot of difference.