I'm making a rolling workbench that will be 34" wide by 60" long by 36" tall. It will need to hold up to 75 pounds of load and the base will need to be open on one side. Because of the overall length of the table and weight of what I'll be working on, I'm planning a center back leg and center horizontal support for the workbench top. Will 3/4" EMT be stiff enough or should I go to 1"? Also, the whole thing needs to be on casters so I can move it around with or without a load on it. Does this mean FIVE casters instead of the usual four?