Ken, absolutely love your 50/50/90 rule! Definitely seems to be how things turn out for me.
I know there are some trees that shouldn't be used because of their chemical makeup. I thought cedar was not used mainly because it takes FOREVER to break down - and that is what you want in a hugelkultur, for it to breakdown and feed whatever you have planted. This link lists the various woods you shouldn't use:
http://gardening.stackexchange...
I think alot of it has to do with what you intend to grow. Your epiphytic plants don't actually draw food from the wood, correct? You are simply using it for something for them to adhere to.
This was my first year to have a hugel. I pretty much flailed around until I had what I thought was right. Mine is small 4' x 8' so if using the chinaberry turns out to be totally wrong I can dig it up and start over.
