If you're using a fixed A2 stock, you won't have to worry about buffer weights. From my understanding, rifle buffers come in one weight, and that weight is ideal for most AR15s. Look into an A1 stock if you're wanting something with a shorter LOP than the A2, since it's about 5/8 shorter, IIRC, and uses the same receiver extension as the A2, just without the spacer that the A2 stock requires. I have a Cavalry A1 stock on my rifle, which I like, especially since I'm a smaller person.
Please note that buffers and springs for rifle tubes are different than buffers and springs for carbine tubes. You absolutely do not want to run a rifle tube with a carbine buffer, nor do you want to run a carbine tube with a rifle buffer. Doing either opens you up to causing permanent damage to the gun.
Anti-rotation pins shouldn't be necessary. Most who run ARs hard in carbine courses and the like never end up needing them. From my understanding, they shouldn't provide any noticeable benefit on semi-auto ARs, especially one that won't be run hard. If the receiver was extremely valuable, such as pre-86 registered FA lowers, it might be worth the investment, but semi-auto recievers are inexpensive enough that in the unlikely event that you start to have issues it could be replaced. More than likely the pins would be an unnecessary expense.
I can't say I know much about precision shooting, nor do I have much experience with White Oak, but I've heard nothing but praise regarding their quality, and they're almost always one of the top recommendations when the topic of a precision rifle comes up.
Congrats on the upper! Make sure you post pics and a review once you've got some time behind the trigger!
