[aenigma]

Well if this is your first system, I would expirement with some basic systems first.But if you really want to do it, the best way is to make your own coaxial condenser like I used on my second cascade system(first was just a watercooled condenser cooled with chilled water).To do that, you take say 15 feet of 1/2 pipe and 15 feet of 1/4 pipe, run 15 feet of 1/4 through the 1/2 pipe.But cut the 1/2 pipe down so you have more 1/4 than 1/2.Now there is 1/4 of pipe in the 1/2 pipe, then 1/4 of empty area.Well use the empty area as the evaporator for the high stage(system a), and the 1/4 pipe as the condenser for low stage(system b)