Yep, handloaded ammo voids all warranty.
handloaded and thinking of 700 yards
Every manufacturer's warranty is voided by handloading that I know of, don't sweat that part of it. Here is my concern: 1)You must have a sub-1/2MOA gun at 100yds to hit vitals reliably at 700 yards. The Mesa has a pencil thin barrel (1/2x28 thread pattern, since you asked), and their accuracy is suspect.
Concern #2) You need 1500 ft-lbs of energy to reliably put an elk down. At 700 yards, you're already below that in a 7mm Remington Magnum with 160 grain Nosler Accubond IF you handload it for 3100 f/s muzzle velocity, which is a STOUT (but do-able) handload.
For about the same money, consider a Browning X-Bolt Long Range Hell's Canyon in 28 Nosler with a brake, or even look at a Tikka in 300 WSM or 300 Win Mag, if you can tolerate the recoil without a brake. You can run a 200 grain Accubond or a 210 grain Accubond Long Range and have more than enough energy at 700 yards with great accuracy potential.
If you want to stick with a 7 Rem Mag, you need a 26" barrel. The Brownings have them in the Hell's Canyon LR with a brake and 1:8 twist. I haven't done the math on a 180 or 195 grain Berger at 700 yards to check energy vs muzzle velocity, but you can run the numbers yourself.
If you're stuck on Christensen, I'd definitely suggest the Long Range version. I would also consider the trigger and read some reviews about this and other parts.
Bergara Premier, Montana Rifle Company, and the Fierce Fury are all better choices than the Mesa unless you just get really lucky. Unfortunately, they are from a couple to $700 more expensive, so you might have to "sacrifice" that Night Force and "down grade" to a Leupold VX-3i in something like 6.5-20x or 8.5-25x to make up the difference without changing total cost. I put 'down grade' in quotes because it"s not really a down grade if you're using one of the most trusted and optically brilliant scopes on the planet.
REMEMBER: A NIGHT FORCE IS HEAVY!!! If you're buying a lightweight rifle to hike mountains, you're negating you're savings in weight by mounting a full 2-lb scope! Leupold and Swarovski are the 2 lightweight, high quality options. Even if you don't agree with my brand choices, consider I am shooting you straight on these considerations.
Have your likes, but do your homework and read reviews and consider scenarios of weight and balance, trigger pull, and sufficient energy at distance. And not the LEAST of which is accuracy potential. You can skimp on a few ft.-lbs. of energy, but you can't skimp on accuracy. Reallistically, 1 MOA will allow you to hit vitals on an elk at 700yds. Maybe not a whitetail every time unless you aim perfectly center mass on the vitals everytime without any variation.
You sound just like me when I was 15, or slightly older. I didn't have access to Internet forums like this. I had to learn the hard (expensive) way - trial and error. You have a better knowledge base than I did, and are years ahead of where I was in what you know. At that age, there isn't much selling trading to be done, so what you get is what you're going to have for awhile. Make the BEST decision the first time. Think about weight, accuracy, trigger, and energy...and your ability and willingness to shoot the gun you pick. You already pretty much know much of this. Also watch for rebates when you start to buy. Browning has some rebates generally every year, though they weren't quite as much this year as in years before. Do look at some of the high-end Tikkas in the 30-cal Magnums. They don't have 26" barrels for the 7 Mag, though. The low end Sauer has great reviews for accuracy and comes in a synthetic version for $750 or a wooden stock for around $900. Also look at the CZ 557- it has a set trigger and some of the most beautiful wood south of $1000 you'll ever see.
God bless and good luck!
And PS. Your 308 is, no doubt an accurate gun capable of teaching you how to shoot accurately. People in the military, and in F-Class have shot with it at 1000 yards for decades. HOWEVER, it has Nowhere enough energy at 700 yards to be a legitimate elk gun at that distance. If you're inside 400 - 500 yards, a case may be made, but not 700 for elk Expansion isn't going to to be optimal, in addition to energy. While you may use it to punch paper at 1000yds reliably with practice and increased skill level, I wouldn't personally use one to shoot a mature elk much beyond 400 yards. As far as recoil, a 7 Mag with a brake isn't going to kick any more than a 308 without one.