I had some fruit bearing plum a few years back. It wasn't quite dry (seasoned) when I got it. It was smaller branches of no larger than 2" diameter and I finished the drying with it laying out in a sunny area for a few weeks.
I figured it was dried enough to smoke with by doing a hatchet chop test. I layed a few braches on a splitting block and gave 'em a whack across the grain. They broke easily, and were easy to slinter. I then took the splinters and broke them in my gloved hands and they snapped rather sharply...very brittle stage.
To chip them I used the hatchet after they were dried out, and just busted them up into pieces the size I wanted. I also peeled the bark off before using it, as I wasn't sure if it would cause a bitter smoke or not, being a very thin bark.
BTW, I found plum to be a very good smoke wood for pork ribs...much better than mesquite.
If you are wondering about soaking your chips, I don't anymore...it seemed to cause more problems for me than good. That's a part of smoke management, which you'll learn when you get started. Takes a few runs with every smoker to find out how they really like to smoke. Just come on back and post if you need assistance with getting a nice thin blue smoke from your new rig.
Good luck and good smokes!
Eric