Your barrel specs are the same as mine, I shoot the 70s out of it and they shoot under 1/2" without a problem. I have driven them up to almost 3200 fps without a bullet problem. I would not use 6 1/2s in an auto, you could end up with a slam fire, they to soft for auto really. I know people who do, but Remington recommends agains it. 400s and 450s are fine, 400's with Varget and 450 with the N140. I have shot some of the 400s for short line and 450s with N550, they both work fine. Contact John, he should be able to give you the initial passord info to get on the sight, tell him you want to start working up load info etc. now. Also, I tried some of the Nosler 105s 2 weeks ago,,,,not a good experience, if you try them, I would suggest jambed to start with those.
On the brass, neck urning is really not necessary, John made the chamber so that it is a no turn neck. Some people do it anyway for the 600 yd. loads. Its up to you on that. I would not do any reaming, etc. until after the first fire forming at least, then you can decide. For xcourse shooting all that will probably not be necessary but some feel better doing it. Sometimes the SSA brass can be uneven on one side of the neck and turn lightly and reaming can help that. Size, trim to length to be safe, chamfer, debure, all the usual and put in some primers, powder and bullets and have at it. Dave