Shamu,
I find it interesting that you picked the name Shamu for your handle here. What prompted that?
Now that most of the full custom, partial custom, factory rifle etc arguments have calmed down for awhile at least I'm curious as to what your bare rifle weighs without the scope or rings or other stuff and no ammo loaded?
I think your choice of 300 Win Mag is a great choice for hunting and if you want to end up with some long range hunting you'll already have a rifle chambered in a very good long range cartridge.
You might want to try a little heavier bullet than the 150. In all my 30 caliber rifles I've ever owned the 165 and 180gr bullets tend to shoot more accurately and seem to hold together better in game but if your rifle is very light the extra recoil the heavier bullets seem to generate can be a bit objectionable.
Also, unless I missed it, I never did catch your discussion of the types of game you intended to hunt with this rifle although you certainly won't be size limited for North American game.