Very interesting, it was pretty much something like this I was thinking about.As to the high availability setup - you might want to check out this site:
http://banoffeepiserver.com/
Seems like he's done high availability on both BPi and RPi. Of course, he's cheating by using an x86 for load balancing (LOL), but there's a lot of information there, including some good performance information.
Now if only I had the money and the time