Just a couple general comments... from someone who is still a beginner and just getting into centrefire PRS and shot a bunch of rimfire PRS.
1) Wouldn't chamber a custom PRS rifle in 6.5 CM right off the bat, sure it is fine and what I use, but the world of PRS is mostly dominated by 6mm cartridges and if I was chambering a custom barrel for PRS I would be researching 6 Dasher, 6 GT, etc... If you are set on 6.5CM, consider just getting a stock heavy barrel Tikka that you can rebarrel later on.
3) ACC is awesome, I have the G2 for rimfire. The ESS is not ideal for PRS as the ACCs give you the long, flat, arca forend with ability to add a ton of weight options for balance. If that is not tactical enough for you (fair enough), consider the new LSS G3 that allows you to purchase different forends and then you could have the best of both worlds.
One other point is do not stress too much over getting a sub .5 moa rifle... not that that would not be sweet. I just shoot a heavy barrel Howa and with a load developed for it the accuracy is fine for a beginner PRS rifle. Getting good environmentals for DOPE, good balance for positions, and a good load developed for the rifle have all been more important for my accuracy... oh... and practice reading wind.
Good luck!
Matt