Hey Grandpa1955, if1955 is the date of your birth, you and I are the same age. Welcome young'un!
Turkey is one of those meats that you can experiment with for decades before you perfect it, usually because you only cook one once a year. I've been the primary turkey cooker since I was 19 years old. I've made some great tasting birds and some that were only good for making turkey salad. Over the decades though I've found that brining and beer canning a turkey, or using a turkey cannon, guarantees moist, delicious meat whether in a smoker or oven.
I often use chickens to experiment with my turkey recipes and have come up with a new brine, injection, and beer can/turkey cannon smoking method/recipe I can barely wait to use on a "fresh" turkey. Not a huge fan of frozen birds. I may cave though and get a frozen bird just to give it a try.
Your plan will work but 6-8 hours might be a little long for a 19 lb bird at 300F, especially one that is splatched, which helps them cook more evenly and quickly. My last splatched bird was about that size and it was done in about four hours at a similar temperature. Are you going to use a Maverick meat probe to monitor the internal temp of the breast and/or thigh? That's the best way to assure when it is done.
If you are interested in the brine recipes I've used I'll post them here. Rubs? I like to use commercial, either Litehouse Freeze Dried Poultry Seasoning or McCormick Sweet and Smoky. I go relatively light on the rubs.
Woods? Pretty much smokers choice but I like a good smoky flavor so Hickory is what I prefer. They all work though so you'll have to see what works best for you.
Below is a picture of the fresh, splatched bird I did last TG on my
Weber Kettle. On a scale of 1-10, 10 being perfect, it was about an 8. Good flavor, crispy skin, but I didn't inject. It needed to be injected to get my brine flavor deep into the meat. If I had done that it would have been a 9.5.
The next bird I'll do on my
WSM with a turkey cannon. Like I said, I can barely wait to give it a try.