I'll go for a couple of these. Are you asking about a straight forward tank or with the ability to raise and lower the water level via compressed air? Compressor running at about 8 bar should do. The air should be oil and water free. Bolts sticking up should be ok as long as the plate you are cutting is reasonably flat. Just make sure the tops of the bolts are as level as possible. A machine torch would be required. A magnetic torch collision device would be relatively easy to make depending on how your are going to do the initial height setup for the plasma. If you are using arc voltage control for cutting height control then do you need an initial height set control as well? If not and you are going to set the height at the start and either manually adjust it or let it cut then the collision device is easy enough. Two machined plates with magnets embedded in them and a couple of pointed grub screws through from the back plate to locate the front plate the torch is on.