I would NOT do what you mentioned, osage/oak/osage. I've made trilams out of osage, yew, locust, mulberry, hickory, hophornbeam, cherry, etc, but to answer your question, what I trust most is Bamboo/osage/osage... straight grained, no ring runout, perfectly clear quarter or rift sawn Osage.
Deflex/reflex, with the reflex accelerating a little bit in the outer limb, like a semi-recurve. That's my favorite. Very stable.
22" riser seems exceptionally long. Longest I've done it 15". Shortest was 9". Depends on bow overall length, draw length, and design.
I don't care for whitewood unless I know exactly how it was cared for from the time the tree was cut. That said, I'm going to a sawmill in about an hour to see what he has. I know he has a nice pile of sugar maple and wild cherry, but ya never know what else you'll find.