Opinions vary, but my recommendation would be to start with an action that has the stuff you want. I have had a few customs built on a trued 700 and they just don't hold the value that a good custom action will. Take a 700 action, toss the trigger, add a bolt knob, add a heavy pinned recoil lug, add a side bolt release, true the action, and you still have a 700 action - just dressed up a bit.
If it is to be "the" gun, start with an action set up your way out of the box, then go from there.
Do it how you want, else you'll be doing it again later.
My 300WM of choice was build by RPRifles here in Texas, his action (rebranded Stiller), rfle basixs trigger, rock 5R barrel, and Manners T4A with chassis. It shoots better than me and loves everything down to 150s and up to 208 Amax. Stillers are tight when new, need some working in, but have functioned quite well for me.
All that said, when I hunted South Africa, I took a Remington Mil Spec 700 with nothing but a threaded barrel and a McMillan HGT stock - and it did right by me, to say the least, very accurate rifle, not expensive to put together. It wasn't a "dream gun" for most, but it was a hammer.