Welcome to LRH, lot's of information here. Read all you can, soak it up. When you decide on your rifle/caliber and scope, then practice, practice, practice. Consider reloading also. It will help you in the long run, in more than one way.
For factory rifles, do you prefer sporter weight barrels or varmint profile? I haven't hunted with or owned a sporter weight barrel in 25 yrs. I, obviously prefer heavy barrels (HB). In that category I can and will recommend the Savage, Remington and Winchester rifles.
Scopes; I own a couple and would go with Leupold everytime. I own a couple of Nikon's and they work fine. In the daylight. Both are fine crosshair, one has a target dot the other does not. Early morning, late evening, they're useless for putting "boolets" on game IMO. I tell people, the bottom line with scopes; if you can't see it, you can't hit it and you sure as heck don't need to shoot at it.
Caliber; this category is as varied as the other two, as most any will do. By that I mean, if you shoot an animal, any animal, through both lungs, it will die. Shoot it in the heart and it will die. The brain, spinal column, same thing. They're going down. Not being a smart *****, just looking at it from a realistic standpoint. None are immune to high velocity bullets.
Most of the bottleneck cartridges, from 24 to 30 caliber, will get you from 0 to 500 yards with little difficulty. Having owned, reloaded for and shot several calibers at the same time, I have found that the trajectory of these is very similar. Especially if the rifle(s) zero is the same, velocities similar and you're dialing MOA.
Consider for instance, the .243 90gn NBT @ 3180fps and 6.5-284 120gn NBT @ 3145 and .300WinMag 185 Berger @ 3095fps, all with 300yd zero's. At 500yds the .243/90 drops 27.9", that's 5.3 MOA up. The 6.5-284/120 drops 26.0" or 5.0" and the .300/185, 24.0" or 4.6 MOA.
Not a lot of trajectory difference there. That's just under 4 inches of difference at 500yds between the .243 and .300. A lot of people can't even shoot a four inch group at that distance. What will vary is the amount of energy on target and on your shoulder. Just some food for thought. JohnnyK.