I'm not that far ahead of you in my own long range shooting "career" so to speak. I've hunted all my life and been around guns, but never really shot them at targets longer than it took to sight in the rifle. I started going to the shooting range last summer. Around Feb of this year, I started going to the range on nearly a weekly basis. My target shooting abilities have gotten considerably better this year. I'm regularly in the 1 to .75'ish area with my gas guns at 100 yards and .75 to .5'ish with my bolt guns at 100 yards. I'm still honing my techniques, and I'm also working on my equipment. I've tried quite a few different rifles, both gas gun and bolt gun, as well as a variety of optics from the $150 NC Star to much more expensive US Optics, Steiner, Vortex Razor. I've had "out of the box" Rem 700's and Savages up to Rem 700 based custom rifles. All of my custom rifles were been used when I bought them. I'm a few weeks out from having my first brand new custom rifle that was built for me. That should give you enough background info about my shooting and knowledge (or lack thereof) for you to determine just how much of my "advice" is worth listening to!
The thing about that custom I have coming to me...... I'm lucky my gunsmith hasn't strangled me yet. I really shouldn't have jumped into that arena yet because I had no idea what I wanted. I thought I had an idea of what I wanted because at the time I had a Rem 700 5R .308 mounted in a JP Enterprises AMCS (chassis) with a Jewell trigger. So I kind of already knew everything. I mean, I had an aftermarket stock AND trigger!!! This is a very expensive hobby, and if I could go back and do it over again, I could've saved myself quite a bit. The mistake I made was doing things backwards. I ordered a "custom" rifle for an elk hunt, which the gunsmith had to set up for me. Once I ordered it, I started camping out on snipershide to learn more, and as I learned more, I wanted to make changes to the build. Gunsmiths don't really like that. I will have to give many thanks to Russell Banks owner of Scout Supply Company for being patient with me and not telling me to go fly a kite by now. I highly recommend Russell, and he would walk you through the process whenever you're ready.
You're on the right track with your .243 and .308. You can learn and practice the fundamentals with those rifles, and through that practice you will start to find out what you like and don't like. And since you have relatively inexpensive rifles, you can easily start upgrading things such as the trigger, stock, optics, scope mounts, etc to learn more about your preferences. The For Sale board here on snipershide will be your best friend on this part of your journey. You can buy used parts to try on your rifles. If you like them keep them, and if not, you can usually sell it and get most of your money back out of it.
Another thing you're already doing that is HUGE is reloading. Since you know how to do that, you will be able to get as much performance as you can possibly get out of your rifles. It will help you learn what makes your rifles tick. Such as how the different barrel contours and twist rates perform based on the different bullets shapes, weights, loads, etc that you run through them, which in turn will help you figure out what barrel you like and will be needed to meet your requirements when it's time to build. The reloading will also help you determine what cartridge you're going to prefer for that 1000 yard rifle. I say prefer, because by the time you're ready to have your own custom built from the ground up, you're going to know about a million different cartridges that could work, but it will all boil down to personal preference. I highly recommend buying and reading "Applied Ballistics for Long Range Shooting" by Bryan Litz. It's easy to read and follow, especially if you're a math guy. Gaining an understanding of ballistics will completely change the way you look at long range shooting, which also entails your opinion on how your rifle will need to be set up to accomplish your goals.
And on that note, I am going to digress for a minute. Figuring out how you will want a custom rifle built and configured to your needs is about much more than just learning the differences in a Manners T3 stock and an AICS AX chassis or Surgeon action vs Stiller Tac 30AW. You need to understand how the entire "system" works on a whole. Understanding how each component of the rifle effects the ballistics, trajectories, flight paths, ballistic coefficients, etc., are the most important concepts to learn. Getting a firm grasp on those concepts naturally progresses into being able to figure out how you would like that custom rifle built. In other words, you have to learn more about shooting than the equipment at first in order to be able to choose the right equipment for the build in the long run.
