IMO, The tried and true .30-06 is the best (for me) all around rifle. You can spruce it up with different barrels, stocks, optics or ammo. You can shoot coyotes and other small critters with something as small as a 100gr plinker or go after moose with a 220gr partitioned or anything in between. Yes, there are many if not hundreds of options in both caliber and bullet types. I reload and I use factory ammo. I can load up something specific that my rifle likes and shoots very accurate or if I forget my ammo and am not close to home or something happens to my ammo, I can walk into just about any sporting goods store and even some mini-marts and pick myself up some .30-06 ammo and continue my adventure. Will it be the exact same as I would have bought at home? Probably not but if I had something of the less common variety I would most likely be out of luck. My dad hunts with a .30-06 and so do several other friends and relatives. Even though I use my .30-06 for just about everything, I still bring a backup. My deer backup is an old Winchester .30-30 lever action. I dont like to see how far away I can shoot a deer or any animal. I like to see how close I can get to it before I pull the trigger. If you want to see how far away you can shoot a deer, why not just go with a .50 BMG? Can go alot farther than anything mentioned before. If you are looking just to make a custom rifle
for the fun of it, then that is great. If looking for an all around rifle, stick with a common mainstream rifle that is customizable. Say for instance, the Win Model 70 or Remington Model 700. They have several different types of barrels, triggers and calibers to choose from.
Anyway, since you are newer to the reloading, I would stick to a common or somewhat common caliber to start with and see how it goes from there. I can take long or short shots with my rifle on a variety of different game. But, this is all just my opinion. I cant wait to hear how the search comes out for you. The thrill of the chase is always exciting.