I charred oak chunks on a propane grill. They were slices from an oak 1x8.
Looking at oak available specifically for beverages, and then looking a oak available from the local lumber sales stores, the priceing difference is striking. The big question is; has the lumber store oak been chemically treated? I would certainly like to buy oak planks from the lumber store if they are safe for beverage use.
The degree of toasting, charring and the rest are all a function of what flavors you are looking for in your finished beverage. From what I have read elsewhere, a propane soldering torch works quite well, burning the surface of the wood to the degree desired, while leaving the underlying wood unaffected. More complexity of flavors that way. Baking increases the depth the heat treatment penetrates into the wood, giving a more monolithic flavor profile.