Re: Deciding calibers?
My recommendation is a 260 Rem. Accurate, cheap, recoil friendly, huge barrel life and Lapua makes brass.
To focus a little more on the switch barrel idea - I have 3 savage actions that I swap barrels around on, the 260 Rem being one. It is pretty simple to change over and takes about 10 minutes. If you screw the barrel down onto a chambered go-gage the barrel always comes back to the same position time after time. I also chamber a no-go gage to make sure I didn’t screw up which I never do but since you are the gunsmith here, you have to make sure.
In particular, the 260 Rem is a Savage LRP. This is a short action target rifle with a no taper target barrel and is a great caliber for lots of cheap practice. You can shoot continuously and the barrel never gets more than warm. It also has a nice HS Precision stock with the aluminum bedding block. However, when I want more punch and a rifle balanced for hunting I switch in a magnum bolt head and large shank 270 WSM barrel. One of the tricks to making the switch easy is using a Warne 20 MOA rail so taking the scope on/off takes about 30 seconds. You do need a barrel nut wrench and an adapter for your vise to hold the action. I built one out of 2” by 2” oak. I also have a standard shank short action and a long action plus barrels in 22-250 Rem , 7mm WSM, 270 Win and 300 RUM. I now think in terms of buying barrels not rifles.