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Dear Nigel, I see you've had no responses to this. Possibly that's because what you propose and describe is a little bit involved. I've looked at it a few times and postponed replying until I had time to get my head around what you propose to do.
Frankly the question in my mind is "why re-invent the step-test, when there are well established ways of conducting them?" The usual way of conducting a well test or step-test would be to pump at a series of different discharges (your 'base rate', 'base rate times two' etc) while recording water levels frequently at first (when drawdown is happening quickly) and less frequently as time goes on. You can either allow full recovery between steps, or pump for a fixed duration per step, opening the outlet valve between steps to increase the discharge, without recovery. You may also want to carry out a longer constant discharge or aquifer test, as this would enable you (a) to estimate aquifer transmissivity, and (b) perhaps pick up any nearby aquifer boundaries which ultimately might limit planned abstraction rates. Standard methods for test pumping are described in the British Standard Code of Practice, the ILRI publication by Krusemann and de Ridder, and in all standard hydrogeology text books. Anyway, good wishes with whatever you decide to do. Richard Carter.