As far as the rifle goes, buy the very best barrels. The difference in price, spread over the life of the barrel is small.
Pick a gunsmith who has a record of producing successful competition rifles, even though that is not what he may be building for you.
Pay a lot of attention to the relationship between brass, chamber, and dies. Work with actual numbers, not terms like SAAMI minimum, or a short throat. Know the numbers, and why they are what they are.
Spend the money for the best bedding.
When you mount the scope, lap your rings, instead of deforming your scope.
Invest in a good trigger.
As far as reloading goes, get a concentricity gage, so that you have a way to measure how straight your ammunition is.
Pay a lot of attention to seating depth, and be aware that the majority of loads produced for bolt action rifles, for match, or accurate varminting use, have the bullets loaded longer than touch. This is not to say that an accurate result cannot be achieved any other way, but you should be prepared to explore in this area.
Have a way to accurately measure shoulder bump, and by that I do not mean using your rifle as a feel gauge.
Learn how to properly clean a barrel, in the least destructive manner. Use a cleaning rod guide, and a good one piece rod, no alluminum rods allowed, except for field emergencies to clear an obstructed bore.
At the range, have something(s) between you and the target so that you can see what the wind is doing.
Try different ways of supporting and holding your rifle when shooting at the bench. Know that a good bench setup will produce a situation where the reticle is not moving at all as the trigger is being pulled.
Do your load development by loading at the range.
Strictly speaking, not all of this is about rifle building, and loading, but accuracy is like a chain that is no stronger than its weakest link.