IMO, there's a lot to unpack here. Don't take offense. If you're new to "long range" than a 30 cal magnum is the wrong choice. I'm all for buying good equipment, and I think purchasing a well built custom rifle is a good choice. HOWEVER, you also need to budget for a good scope & mounts, good accessories (rangefinder, bipod, rear bag, tripod, weather meter, chronograph, cleaning equipment, shot timer, etc., etc.). AND lots of ammo. You can get really far with focused & intentional dry firing, but you will need to get a lot of live fire reps in to become proficient. Depending on your overall budget, you might need to start making compromises somewhere.
In terms of barrel life, yeah barrels are tires & need to be changed, but to start out I think you should look for a moderate cartridge that will have +/- 3,000+ rounds of barrel life. Plan to shoot the same bullet and learn it. Starting out, look to get 2,000+ rounds down range your first year (which is only about 40 rounds a week) and probably 10x - 50x that in dry fire. It's not 'sexy', but focus a lot at shooting 100 yards on paper, take notes & pictures & track your data, and work on positional shooting (look up Kraft drill for an example). Take your weather meter everywhere. Guess wind speed/direction and then check with your weather meter to build your internal database. I'd also avoid reloading in the beginning as it just adds unnecessary variables, time, and cost (and most reloaders can't outshoot quality factory ammo anyways).