I have experience with hydraulic line pressures up to 10,000 PSI and one thing for sure is that you are in dangerous territory for an amatuer rig. The placement of a plywood barrier, although sounds good may offer little protection. I had a failure send a projectile over 100 feet then through a box of plastics then into a rack leg denting it. It spun past me like a speeding bullet. There are electric motor pumps that are most dangerous because they pump very fast and high volume. There are hand pumps that control the pressure much more and are recommended for this type of experimentation. If a leak developes, stop immediately, do not try to prevent the leak just dump the pressure and do not continue. High pressure hydraulic leaks can cut through skin like a hot knife through butter. Low pressure hydraulic leaks can push hydraulic fluid through the skin and lead to a nasty infection or worse. I believe like others that this is not going to work. As a little experiment, take a full aluminum beer can, don't shake it and try to soft dent it with your thumb. It will not dent. Now take that same can and use a ball point pen to put a small ding in it. Shake the can and that ding will not move. Small dings are very hard to remove with internal pressure. Good luck and stay safe, cheaper to replace a frame then to pay for one hospital stay.
Ray Homiski
Elizabeth, NJ