Sorry for the slow response and the Savage makes a great action for building a LR rig. I've never put together a semi-custom rifle
before but I do own a 112 BVSS in .300WinMag and have owned a couple of 110 FP's. With load development the stock rifle can be made to shoot under 1/2". I have always preferred long, heavy barrels so there's never been a great need to screw another on the actions I've had.
You can buy pre-threaded/chambered barrels from a few barrel makers; Shilen, McGowan, Pac-Nor and Lothar Walter. With a little knowledge, simple tools and go/no-go gauges you can install the barrel yourself. Some prefer to let a competent rifle-smith do the work.
As for the stock, there are a lot of options. Some of the favorites listed on this website are McMillian, HS Precision, Joel Russo, Bell and Carlson, Hogue, Richards. The list goes on for quiet a while. I like the stability of synthetic stocks with aluminum bedding blocks but love the looks and feel of the laminates, which also make great platforms with pillars and bedding. Again, the choice is yours.
I'm pretty sure 1000 yds is very doable with the .300WSM. Others on here speak highly of the cartridge. A mile, hum, I have no clue. Maybe some of the other REEEAAAAALLLL long range fellows will chime in (they maybe busy driving from the bench to their targets!
). Good luck with your decisions and let us know what you end up doing. JohnnyK.