Best way to be comfortable shooting from a stand is practice. Set up your stand and a target before hunting season and shoot from it.
I set my stands as low as 12ft and a max of 25ft no need to head for the sky. Set your stand so you don't solute your self. Have another tree behind you or don't go crazy cutting tree limbs.
Yes, you can hunt a stand right away. I have had success setting stands in the morning and hunting them that afternoon