Re: 300 rum build
Welcome to the site. Hope you find it to be a cool place to hang out.
Your list sounds pretty well set, should make a heck of a rifle. If you haven't decided on which brake, I can highly suggest one from either Defensive Edge, which my bud has on his 300, or one of the Allen Precision ones. Either will tame it down to pussy cat levels.
On your optics, myself having both mid power, and high power scopes for shooting out to 1K, I highly suggest keeping your top end at 18x or less. What you will find, as I did, is the higher powers are great out to around 500yds or possibly a bit further depending on where your at. However, and again depending on where your at, or even what you might be looking out across, once you get above that your going to loose the use of the higher power during most of the day due to mirage. I use the 5.5x22x50 Nightforce, and here in the balmy south portion of Texas, once the sun gets up your on borrowed time while on 22 power. I have found that with the humidity we have, during mid-day sun or heat, about the most useful year round is 16 - 18 power. Even at these power levels it can still be a bit much to chase the spot around in reticle. The 22x is very nice to have when working up loads or getting a good look at something out to around 400 or so yards, but with the 3.5x15 I have, I can use it effectively all day any day out to as far as I can settle the fine cross on.
One thing also to consider is that most of the mil dot type ranging scopes are calibrated to a certain power, like 10 or 12, so be sure you consider this when you order, as it might help you decide on one over another.
Telling you to get X,Y, or X, brand is like telling you to get a Ford over a Chevy. Most of the top name companies put out awesome glass, and rarely leave you wanting. However, what is clear as crystal to me night be a bit off to you, or one brand might be calibrated in Minute Of Angle and the other in Inches Per Hundred Yards. Either will hit what they are tasked with, but one might be easier for you to use over the other. If your using a calculation program like Exbal, they can use either to work your drops with, but you have to remember to make sure your set which one your using, when you do your drops or it will throw you off.
Good luck with your build it sounds like a great project.
Mike / Tx
"Heck why would I lie, most folks don't believe the truth when I tell them"