I don't think it was the wood.
Never used his rub, but personally I don't like a lot of paprika in mine. Just don't like the taste, little is good.
Where I think you got your bitterness from is the method of adding unlit charcoal to the smoker. This is just my theory, but I came to it from making changes to my cooks. I used to do the same thing.
On this site there is a lot of information on modifying the
WSM style smokers. Take some time and see what others have done. Look for a charcoal basket mod. This will help keep a cleaner burn for a longer time. What I think happened was when you added the unlit charcoal to your cook chamber, it takes time for them to all get burning clean. So for the first 30-45 min you are seeing a very thick white smoke. In the thick white smoke you will have creosote in it. If too much creosote gets on the product it will get bitter. I would also look at removing the water from the pan and adding playground sand covered with some foil. This will give you a heat buffer as well as a stable heat sync for your cook chamber. Water will keep absorbing the heat and energy without releasing much back into the cook chamber, so you burn a lot more fuel to keep your temps up. Also when you add cool/cold water to the pan, you spend time and energy to recover to a proper cook temp. Sand or a solid mass like lave rocks will maintain its temperature and release more energy during the cook, so you burn less fuel.
Just my thoughts.
Jeramy