From the ground up.... consider:
Set up to shoot prone... precious few ranges let you shoot to 1000yds and further from a bench. Never met a portable bench that was as stable as terra firma. Most have access to crown land and out in BC, logging has created miles of open terrain to play on.
Look at the FTR type bipods for peak accuracy AND if going to larger cals, ones with less moving parts. Wobbly, sprung bipods are so much harder to use when precision ELR shooting is desired. Pedestal rests work too but more of a pain to set up and carry.
Rifle - peak accuracy is NOT that big a deal wrt to ELR shooting. Consistency and stability is far more important. Sub MOA is the goal... less is great but don't sweat on the cost to build a 1/4 min rig (not to start anyways). Know what the barrel does as it heats up. It is super easy to chase the puff of dust and barrels get hot... many factory barrels start to warp or change tuning so now you are wasting ammo chasing ghosts. What you need is a rig that is dead stable from cold to as hot as you run it. "stress" test the rig.... at 100 or 200yds, put aiming points in a horizontal line and shoot 5rds groups at each. Look for any change in POI or group size from 1st rd to shots 15 and 20rds at a 15 sec pace per shot... yes, the barrel will be screaming hot.... may as well know now before wasting alot of time missing in the field.
LR wind doping is all about trusting your gears cone of accuracy.
Ammo - spend lots of time here making the most consistent ammo with the lowest vertical (use the best scales you can)... this is what kills you at ELR distances. You want match quality handloads with the right bullet. Lots of info on my website. Even factory rifles will benefit... garbage in, garbage out and very slight variations in your trajectory is going to drive you insane at long distances. I call it ping pong... you can put bullets this side, then that side but no matter what you do, it just doesn't seem to land in the same place twice.
The high and low ping pong is the most painful....
Bullets - many new gen bullets are designed for super sonic flight and suck at transonic/subsonic flight or need non conventional twist... TEST, TEST, TEST
Optics - Use a scope with a record of tracking properly, reliably... These show up at F class matches. You do not need to spend quantum bucks.. just depend on brands with the right engineering. Many scopes have wonderful rating on elevation adjustments but optics tank at the extremes of travel. Spend time here to learn what works and what is just bling. Learn about a tall target test... lots of scopes fail this. Glass that can see mirage will be extremely helpful unless you plan to shoot with a spotting scope that can.
Mirage is you friend!!!!
Base and rings - use quality products.. lots to choose from. I prefer steel on boomers or high rd count rifles for a base. For rings, Burris rings with inserts are SOOOO easy to use for setting up the shim you need. The further you go, the more important proper scope zero becomes. Mechanical bases are interesting but really not needed until you break the mile...
Cartridge - Having pushed a 223 to a mile, there are so many options today to get into ELR shooting. Bigger is usually easier to drive but many mid size cals (6.5 and 7mm) work superbly. Even the 6BR can be an effective 1 mile gong smasher with the right bullet and set up. Just keep an eye on costs. When you are in the field LR shooting, you can burn up alot of ammo (50rds is not much) so cost of ammo and rifle wear becomes very important. There are lots of 50BMGs, 338LM's sitting in closets.
Muzzle velocity is only important if you are going to limit distances to whatever the supersonic flight is... this gets real expensive real fast if you want to go well beyond 1000m. I much prefer to use a bullet that will go subsonic... eventually, EVERYTHING goes subsonic. A club in Montana/Idaho shot 308's to 2km... really loud lawn darts.... big target on the prairie floor
wind drift... yeah, it is going to move and huge amounts. Put up as many flags as you can... wind changes direction and intensity over large distances. Shoot into large open terrain with hopefully grass or dirt so you can see the dust kick up with the bullet arrive. Don't worry, even an 80gr Amax kicks up dust at 1 mile....
The work is done at 300yds... beyond that, it is up to shot delivery, bullet stability and your ability to figure out what the wind is doing. Don't get too hung up on target size as you get way out there. 1/2 min at 300yds, might only be MOA at 1000yds and maybe 2.5 MOA at 1mile. Things are going to move around. Part of the fun of ELR shooting is actually hitting the target....
Shoot, shoot, shoot... don't get hung up that your smart phone is not all that smart. Gravity and atmosphere never got the update. Focus on gear that is reliable and repeats... everything else gets tossed.
Jerry