My humble opinion is that MRAD vs MOA is totally a taste thing, either one will suit your needs just fine. I have used MOA exclusively and I calculate everything in MOA (Even though we use metric in Austria) so for me I see no need to change to MRAD. Thats pretty much all I can say about this. As for the scope, definitely a good choice which will serve you well for shooting at those ranges, good quality and First Focal Plane is good for using the range markings and 25 power is excellent for this task.
The only thing I'm a little skeptical about is your caliber choice. While .308 will definitely get out there to 900-1000yds and its definitely one of the best, most readily available precision calibers out there it will
barely go out to 900-1000 and any adverse conditions will affect it much more than more suitable calibers. Also the 308 drops a lot at those ranges so you may have to invest on a titled scope mount, there are mounts that give you 10-20 MOA additional elevation adjustment. If you plan to shoot at those ranges I'd go with a 20 MOA tilted mount right away.
Personally, if I'd shoot at those ranges
frequently I'd go with one of the magnums and start handloading. That makes shooting long range SO MUCH MORE pleasant. With handloading I can DOUBLE the accuracy of my rifle even when using high quality match ammo, and it makes shooting the big magnums as cheap as shooting commercial match .308. If you want to shoot competitively you have no choice but to handload anyway.
If you plan to start to handload I'd go with .300 Winchester Magnum, 338 Remington Ultra Magnum or with the .338 Lapua Magnum. Those will drop significantly less and buck the wind much better than .308. If you plan to shoot mostly 400-600yds and go out to 1000-1100 only every once in a while I'd go with the .308.
I had a 300 Winchester Magnum which I loaded with 240 grain SMK's at 2600fps, boy that was a screamer, shot like a laser and the 240 pills looked more like torpedoes than bullets, they were that long. They just did not decelerate.
Left to right: 150 grain FMJ, 168 grain SMK, 220 grain SMK and the 240 grain SMK. Imagine the 168 bullet typically leaves the muzzle of a .308 at 2600-700 fps, now the 300WM will shoot the 240 grain bullet on the far right at the same speed.