If you plan on using chunks, figure out what your going to place them in. I use an upright coffee can drilled w/holes for air, and I mix RO lump and two chunks per load. On the size of the chunks, this might be dictated by what ever you'll use to place them into. Generally speaking, you'll use chunks no larger than your hand, or even a little smaller. Whatever type of wood you use, go easy. Too much wood can create creosote, which is a health hazard to avoid. If you have large clouds of white billowing smoke, you're burning too much wood at one time. Go for the Thin Blue Smoke. It's all good my friend.