First I am the LAST person who's advice you should take first.
That being said 800-1000 yards is more then a different ballgame its a whole new sport.
Learn the fundamentals at 100-200 yards. Stance, breathing, judging wind, distance etc. Go to an Appleseed shoot and or get some professional education. Just be aware that shooting at that distance is not something that is simply equipment dependent. At that range you are talking software and hardware.
.308 is a good, mainstream caliber that can be loaded or bought in very accurate packages. Good all around cartridge IMO.
Get the software up to speed before you spend big bucks on the hardware.
Just my uneducated two cents. Says the guy who can barely see 200 yards and thinks .75 inch at 100 yards is just damn peachy keen.