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Does it make much difference whether I go for bolt on or center lock?
Not much. I prefer 6-bolt because it's simple and more widely used, so new rotors will always be cheaper and easier to buy. I haven't seen how centerlock holds up long term, but I'm concerned that a sliding fit spline will be prone to fretting which will destroy the expensive part (hub shell) just as fast as it destroys the disposable rotor.
Which axles? For QR, you should be able to find Shimano M525 in 36H/Silver