Everyone smokes as to how they like their end result. When you ask a ford man its a Cobra GT, as a Chevy its Vette. Its whatever you like. I spent 30 years injecting before I ever brined. Personal preference. Suggestions for injections; keep it simple. Use a cattle hypodermic needle instead of the huge shoot out the sides things. Make lots of holes and use little juice in each one. Puddling is not a pretty sight. If you trying a new injection always best to go in conservatively. Everyone appreciates a little added flavor, nobody like to bite into a pool of garlic juice. Keep your injection not cold, it injects better. Also unless its a cheap no name turkey you probably don't need to inject butter. It hardens and pools. Keep a warm glass of water to put the hypo in to keep it warm while injecting.
My Dad always rubbed "Kitchen Bouquet" sauce all over the bird before he'd oiled it up with suntan lotion. He said the Kitchen Bouquet helped smooth out the color of the skin so the little scraps and scratches are not noticeable.
I assume 300 is because you are planning on crisp skin. It depends upon your smoker. I can smoke at 300 and my skin is rubbery. I can smoke at 220 and the skin is tender, but definitely not crisp. Best way to ensure crisp is to transfer to a grill or oven. An electric doesn't crisp any better than it imparts a smoke ring.
If you are going fruits instead of vegetables, you can also handle an aromatic like thyme or lemon grass maybe? I did a chicken a couple a weeks ago with apricots, it was totally awesome. If you use fruits you might also look into possibly adding some to your injection. Not a lot nothing should overpower your taste buds, but you should be wondering where that taste came from you just enjoyed.
Be sure and let it rest min. 6 hours refridge after injecting so that it can be better absorbed into the meat. Over night is best. And don't forget to rest after removing it, meat tastes better when you have not burnt your taste buds.
Look for sweet fruity woods to smoke with and don't over smoke it. You are not smoking to hang it for the winter, you are smoking to enjoy that taste.
Anyway, Those are some things I would think upon. I am sure there is more but you'll take some notes this time and the next one is even better.
Hope ya have a great smoke and remember what a wise man says, Patience. (I can't believe he missed his chance to say grasshopper there). Enjoy the smoke, its not work, enjoy it.
Good luck and good smokin. Its all about personal preferences, you never finish refining.
Please come back and let us know who you did, better yet show us.