If you want a really nice top of the line super rifle, you should buy yourself the best 338, 50BMG etc that appeals to you. What you have in mind sounds reasonable to me.
If you also want to learn how to shoot well at long range, you should buy yourself another rifle too, in addition to the aforementioned "super fun rifle". You can buy this "learning rifle" at the same time, though there are some advantages to buying it first (one of them being that after you've fired a few thousand rounds through it it might help you better decide exactly what you want in your "super fun rifle").
If you are (or are interested in being) a serious accuracy-oriented reloader of rifle ammunition, there are quite a few choices for this "learning rifle", but the best two I can recommend are a fast-twist .223 or a medium-twist .308Win. If you are going to reload your rifle ammo only to keep things affordable, i.e. you reload to shoot and you'd like to avoid making reloading a hobby in itself, that narrows things down considerably - the only really smart choice would be a .308Win. There is good accurate factory match ammo suitable for long range available for .308 (though it is expensive), and handloading long range match ammo for .308W is more straightforward than most other cartridges.
A .308Win (and if you are a precision reloader, a fast-twist .223) are not ###y choices. But they are fully adequate for shooting out to 1000 yards, and have many advantages over higher performance calibers such as .243 Win, .260 Rem, 6.5-.284, .300 Mag, etc.
* very long barrel life
* more easily achievable top-notch accuracy (you can't learn with an inaccurate rifle!)
* with the correct bullet choice, their ballistic performance is sufficient for shooting out to 1000y
* at the same time, their lower (than .260 Rem etc) ballistic performance is actually an _asset_ when it comes to learning how to shoot at long range, what the wind does, how groups form, how to get the best results under a given set of conditions.
If you learn how to shoot a .223/.308 such that you can hit anything, every time at 600 yards and most of the time at 1000 yards, you will be able to take a .338 or a .50BMG and be able to perform similarly at 1000 yards and 1500 yards. More than just delivering shots safely and controllably from these big boomers, you will be able to deliver long range shots masterly.
