Hi, it all seems fine, the plugged in mcb will be a type 2 which is the only ones available to fit the wylex boards, with the load & distance quoted I can't see a problem.
As for RCD, yes effectively you fit in line with L & N and if fitted in a good enclosure there will be some where to terminate the earths
MCB's act quicker on overload and slower on short circuit than fuses if you change all fuses for MCB's you may find on the odd occasion the MCB will trip when light bulbs blow. But since they can easy be reset overall I would say it would be a good thing to replace all fuses with MCB's I did and never regretted it.
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