Thankyou for your responses. They are most informative and give me some firm guidance.
Initial thoughts are that I shall only process each film type on its own. Am happy with idea of 6 sheets per batch. Will become less economical if I have different pushes to perform. One sheet per tank is quite wasteful.
Presume that I will have to see what tanks the machine itself comes with. Jobo make big claims about the Expert tanks, but they don't seem to appear second hand. Is this because they are so good? The idea of high levels of randomness does appeal!!! Having never seen either type of tank in the plastic, it is even harder to make a decision.
Are there any tell-tale signs to indicate how hard a machine has been used?