I'm a wee bit late to this party, but if you haven't found the toilet yet, you might consider checking out FamilyBus' posts, if you havn't already. He has 6 kids too and uses a composting toilet- i believe he just uses the sawdust bucket. He's quite knowledgeable about electric and power options too.
For some really good ideas on the propaneless set-up, I think you may like wmkbaily's build thread "The Journey Visni" (sp?). After his roof raise, he rigged up his Webasto for heat that would run with a marine heating system, plus LOTS of good pics, sources and details about how he set up the AC/DC wiring and battery banks, isolation switches etc etc
You mentioned different metals for different projects. Don't forget about galvanic corrosion. Here's a good info sheet. http://www.engineersedge.com/galvanic_capatability.htm
(even though the address is spelled wrong. Oy)
Nimbus 2000- Great name!!! You should edit the name of this build thread!
Love your bus-bucks idea! Brilliant.