Re: getting started,new to board
Axe, lets start of by saying the 280 Rem will certainly do what you want out to 700yds. I have a friend who shoots LR (1000m) with me and his 280 is very impressive.
From his experiences, I would make the following suggestions: Bullets Hornady 162gr SST/Amax, 168gr MK. Powder: Re 19, H4831SC, maybe H4350. Primers: Fed 210M or CCI BR2. Cases: matched prepped commerical stuff (he uses Rem). Ammo must have min. runout (under 4 thou). For sizing, I love the Lee Collet neck sizer. Most seating dies are just fine. If runout during seating is present, go with a Forster BR seating die.
Rifle: assume that all the basic tweaks are done and the rifle will consistently shoot MOA or better at a min of 250yds/300yds. Forget about testing at 100yds. That distance will not show stringing. All you really need is to be able to hit a milk jug everytime at the max distance you want to shoot. BR accuracy is not necessary, just consistency.
Scope: Shim scope, if necessary, so that you have enough elevation to get to 700yds. Your scope is fine but will need turrents (contact Wideners) for elevation adjustment. I love Burris Sig rings but you can also get some shimmed bases (Farrel are great for the price). See how much more "up" you have left in your scope from a 100yd zero. If you have around 20 min, you should be fine as is.
Rangefinder: you are going to need one and I would look at the Leica 800 now on sale. The best rangefinder and will work well at 700yds.
Spotting and bino: spend money here. You need to see the game to shoot at them.
Work up a drop table (lots of info elsewhere) and practise, practise, practise from field positions/rests and conditions. 750 to 1000rds in your first year is not excessive. Doping the wind is your biggest hurdle. You must be confident in your ability to hit that milk jug (I make up swinging metal targets) in order to responsibly take a poke at a deer. Range a "rock", dial up your scope, judge wind/light, take one shot and call the hit. Keep changing targets and ranges to ensure you can hit close and far, also that your scope is repeatable and your drop table accurate.
You must have that confidence in your equipment and your shooting ability. Shooting LR is no different then SR. Marksmanship/doping the wind is everything.
You are now well on your way to happy poverty as you acquire more widgets, rifles, and components. Enjoy the journey. The company is pretty great around here too.