First to weigh in on the 50 or 56mm on the NF scope........I have one of each and really can't tell enough difference in low light or detail resolution to matter. The 50 weighs less and you can use shorter rings.
The other guys have given some great advice and I won't repeat any other than to say as far as I am concerned the Swaro range finder can't be beat if you can afford it.
The other things to consider that have not been mentioned yet is what you need to get steady in a field situation. When you step into true long range hunting/shooting it should be a "given" that your crosshairs are rock steady on whatever you are planning to shoot at whatever range you intend to shoot. There are too many other factors to worry about, your crosshairs bouncing around should not be one of them.
This is where some "practice" time in the floor will come in handy. Many on this site shoot off a bipod with some type of rear bag and that is a good choice. You need to spend some floor time getting comfortable with whatever method you chose to get comfortable with it. I often carry a fairly heavy tripod for my spotting scope. I have fabricated my own rest I can clip on my tripod, and I use a Stony Point bipod on the REAR of the stock so I am fully supported front and back. I find this gets me just as steady as prone with a bipod and a bag, but gets me into a sitting position so I can see over low obstructions. That type of setup may not work for you and I am not even necessarily reccomending it, I am just saying it works for me and you need to spend the time to find out what works for you. The time to figure out how to get steady is NOT at 8,000 feet with a critter on the other side of the canyon