was not reading this back when you originally posted it but I just read through and found some very interesting and useful info.
on the 24 volt supply I have found using two computer power supplies works to provide me with that from their 12 volt out lines. I just tie the ground of one to the positive of the other and then run positive from one to my positive on the item needing power and ground from the other one to the ground to the project. you only get the amps of the lower of the two, but you get the full 24 volts. *used this to make an anodizer for stainless and tied 10 units together at once to get 120volts of DC power, and it worked just fine too so....* being DC the outputs of the powersupply can be used much like batteries for getting more voltage or amperage by using them in parallel or series (par for more amps and series for more volts) Just do not try to use that with the outputs from the same powersupply, as that will blow it out by shorting the hardware.
MDF is great by the way and I find I get a lot more strength by using thinner layers and firmly clamping evenly the parts after evenly covering the joining faces with wood glue. this creates a sort of skin for the layers kinda like the fibers in fiberglass and makes it stronger. I am even considering using fiberglass in a set up at some point too, to bond the layers of MDF and see what I get.