For white tail I would go with the 7x57. The 7mm Mag is best left for someone that has more experience with shooting. For many new to that round it can start a habit of flenching that can extend to all center fire rifles one shoots after that.
I would also suggest if funds will allow, and it is legal with your state's game laws to look into a good used .243 Win bolt action, or one of the affordable package rifles. After sighting one in, they are good to go on white tail deer out to 150 yards (maybe more, though I would stick in the 100 yards area for comfort.) Also if sticking to 100 yards or less a good used lever action in .30-30 Win is also a good rifle. I stated those two due to the fact that you can find ammo for them at most any place that sells ammo. You stated that your stepfather is the reloader. I stated round that you can buy yourself.
Another suggestion would be to instead of purchasing new equipment find an instructor, and pay for a few one on one sessions. I think that would be the best route to go. It is what I would suggest to most people.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.