Start with a small quantity of bark, whatever you choose. This will give you an idea of what you're dealing with without dealing with large quantities of material, which can be more of a problem than the actual chemistry involved. If you just want to get some DMT, I'd recommend an STB, but if you want to start learning extraction, I'd go with doing an A/B and an STB side by side with the same quantity of identical bark and decide for yourself how you prefer to work.
After that, you can step up to the more advanced procedures, exotic solvents, and experiments if you want, but get the basic chemistry and technique down first.
Good luck, be safe, don't throw anything away, and post your results!