Hey Joan,
I've seen lots of Multi grafts here in Sonoma. Seems like the trick to those is to prune back the vigorous grafts so the less vigorous grafts get a chance to establish. They seem to be growing pretty well.
As long as you understand pruning you can train them pretty easily. I've been lucky enough to have John Valenzuela as a mentor in that dept. Espalier require pruning as hard as grapes, cutting back to a spur every season. You can prune trees back really hard, especially if you're training them for a small space. Just pick a bud going in the direction you want and prune it at that point.
When I was in Malibu, I got a lot of my trees from OC nursery. They were mostly wholesale, but you might be able to get them to sell to you. Purchasing bareroot is best, but it's too late for this season. When ou get a new tree, you should really prune them back hard. You can make any plum into the fan shape, just prune it back. You can make any tree a dwarf if you don't mind pruning it back hard. Alex Silber at Papaya Tree Nursery in Granada Hills can be a great resource as well as Exotica in SD.
As for Ice Cream bean, I've had these in Hawaii. They're OK, but not my fav. They can get big, they produce Nitrogen. I used to prune them really hard every season and use them as a chop and drop for my other trees. Handy to have around. Chickens like them. They may take more water than you want to give them though. A better local N-fixer could be Carob, ceonothus, acacia,catalpa, locust, etc. Good luck on your new plantings!!!
Say hello to LA for me!!