I'm not officially an expert (yet), but I have enough experience and have read enough to provide an answer to your question. If the bird you bought is already brined, brining it more will make it too salty. Definitely the slaughterhouse brine will be too much.
Since your meat says 8%, that's on the low side of pre-brined birds (that I've seen), you might be able to liven it up a little by making your own MILD brine to add some flavor without lots of salt. I did this once before I understood brining and it was actually amazing! DO NOT TRY THIS WITH A WHOLE TURKEY. The dark meat gets way to salty even if you're only adding a little more. Turkey breast is ok.
I would try a solution with say 2-3% salt, 1% sugar (brown sugar preferable), a large onion (1lb+ diced), some coriander seeds (1Tbsp), peppercorns (12), bay leaves(6), and all the leaves from one bunch of celery (diced).
Boil that all together then let cool, use ice cubes if necessary to drop temp quickly. When brine gets around 80 degrees, put your bird in (breast down) and put it all in the fridge (or outside, covered, if 50 degrees or colder during the day). Soak for 24+ hours in that solution and then dry it (paper towels) and hang it in the fridge (or rest on a cooling tray with a pan under it) for MINIMUM 12 HOURS.
With a turkey breast, they cook fairly quickly, so I like to do low-temp smoke until the breast is over 100 degrees (breasts up). My smoker (GMG DB Wifi) can smoke as low as 150 degrees. A 10-pound breast will take about two hours at 150 degrees to get from fridge temp (40) to 100 degrees. Then I turn the smoker up to 350 and smoke it until the breast reads 155 and the thighs are around 170 degrees (~2 hours). DISCLAIMER: The FDA says you should cook turkey to a minimum internal temperature of 165F. I then pull the meat out and let it sit 15-30 min at room temperature before slicing.
With this process, the skin may be a little chewy. The dryer the skin before smoking, the better. I've heard that another great idea is to BBQ the turkey breasts-down for 10 minutes on high-temp before starting the smoke cycle. As a pellet smoker, mine can do that without any issues so I'm planning to try that approach this Thanksgiving. (I'm spatchcocking a 27-pound bird), look into spatchcocking if appearance on the table isn't as important.
In my opinion, smoked turkey is one of the finest meats on the planet. If I can't have lobster or crab, I'll take a well-smoked turkey. Good luck!
