Already, I have re-potted around half a dozen with a mix of really free draining potting medium - mostly sand and gravel & very little peat. What goes completely against the grain is keeping them so very dry. Given that we're moving into winter, I figure I mustn't be tempted to water them. My plan is to identify and label them all so that I can get to know how to deal with them - as individuals.
Meanwhile, the top shelf in the greenhouse is looking rather desert-like. Oh and I did treat myself to a special pair of extra thick gloves which cope much better with the spines!