Welcome to LRH. I'll offer up some opinions on the direction you are headed, but please keep in mind that my opinions are usually worth no more than what you paid for them.
1) The big 338's don't add much to the equation until you get out past 1,200 yds. That is where the really begin to shine and leave the smaller calibers behind. If most of your shots will be 1000 yds or less, your 300 WM will do just fine.
2) 8-32x50mm or 56mm is a lot of magnification. Most find the 5.5-22 more than sufficient.
3) For a long time, I ran a Swarovski rangefinder with a Kestrel 3500 and JBM Ballistic software before switching to the Shooter app. Last year I purchased a G7 BR2 rangefinder to simplify things and cut out a few steps (precious time) in getting a firing solution. I'm still learning the "ins & outs" with the BR2, but overall I am pleased. I still use the Kestrel for wind readings and Shooter as a backup when time permits.
Good luck in your pursuit.