Re: A new 300 RUM
You get what you pay for. If you cut corners now you'll pay for it later. Go with a Manners stock or a McMillan stock, or an AICS. Any of those three will serve you well, and there are none that are better (McRee is another). Stick with a standard Remington trigger and have it tuned, Jewell's (HVR, etc) are very tight and can malfunction with dust, dirt, etc in the area. As far as the barrel, 28" might be a little long, try 27" and put a Badger Ord FTE on it, it'll get it to 28" and tame the recoil down. For manufacturer try to stay with Schneider, Obermeyer, Rock Creek, Lilja, Hart, Krieger, Bartlein, Broughton, or Benchmark. There are others yes but the small difference in price isn't worth it to skimp, buy the best and shoot it out. Seekins makes excellent bases and rings, along with Badger Ordnance. Badger Ord also makes the M5 DBM, a good idea if you want to shoot it outside of hunting, but not necessary per se. Optics are a whole 'nother thing.
PM me if you have any questions.