What I found with the vertical split in the hopper, is the fire will travel up the split faster than it travels up the charcoal. The split will be completely consumed but the charcoal around it has yet to ignite. I've gone back to layering chunks and putting a couple chunks in the ash pan on a grate. And i add wood to the ash pan during the cook.
As for sourcing wood, the best wood is from a local wood lot, if you have one. Find out where the stick burner people are buying wood and see if you can buy in small quantities. Then cut your own chunks. Here in OKC, we have a wood lot that sells small splits , maybe 4 X 4 stacks of roughly 12" long splits, for $50. I run a stick burner and that will last me a long time in the offset.
Or just keep an eye out for anyone cutting or trimming hardwood trees. All it takes is one pecan limb and ya got enough chunks for a lot of cooks. The best thing about that , is you know exactly when it was cut and how long its been seasoned.