After working with diffrent holster set-ups on my leg, hip and pack, I chose to go with a set up that will allways be on my person while in camp or taking a poo. Diamond D Chest Rig with a 629.
They can be up that high but it's more of a question of habitat at 10k that your hunting in more than pure elevation. Thick timber, water, food and overall terrain all play a key roll.
Any training is better than none.
Focused training is better than just any training.
Start with broad strokes if your just starting out and narrow it down to specific goals you need to progress in your chosen field.