If you're expecting to press 5 gallons of Apples at a time I think you will fall quite short. Unless you take a more commercial approach to the press design, the surface area to volume ratio of your press will limit its ability. I.e. if you press a quart at a time, you will get more juice in the end than doing a gallon(or more) at a time.
You may be able to crank out a lot of force, but eventually something will break and it won't be the apples lol.