Sounds like you're set. The bullets you chose should be fine. I would be tempted to try the Woodleigh,s both Weldcore and the Hydrostatically stabilized bullet as it may be more disruptive than a conventional solid. The Weldcore is a good choice for herd situations as an on the shoulder shot will usually stop on the hide on the off side. You can order directly from them so should be available.
R-16 is showing promise in the 375 H&H for me, might work well in the 416. Top velocities and temperature stable. A little faster speeds than R-15 which was my previous go to.
Not a major issue but if you find accuracy a grain or so below max I would stay there. Always good to have a margin of error for hot weather shooting. Full length size each case for the same reason and cycle all of them through the action.
I would get some Hornadays or the ACP for load work up till you do the final load tuning.
