Sizing of RCBO

Need a bit more information about the type of appliances likely to be plugged in to the sockets. Also the cable size and the installation method(s). The sizing of the overcurrent part of the RCBO protects the cables, not the loads. So if overloaded it trips before cables get overheated.

The most common approach is to utilise a standard circuit. Very often a 32 amp circuit for a floor area of up to one hundred square meters, or sometimes a 20 amp circuit for a smaller area. Other arrangements are possible though.

Cable sizes should be determined by a suitably experienced person and depend on a number of factors.

Double check that the proposed RCBO is a true RCBO that provides both overload protection AND earth fault protection, an RCD that provides ONLY earth fault protection is NOT suitable unless used with a suitable fuse or MCB that provides overload protection.

Further to that 100m2 per 30A circuit rule of thumb,  if the area served includes a garden, then the figures need a bit of modification. Adding a socket for the lawn mower may in a sense add an extra few hundred square metres to the area served, but the load does not scale.
Note that sometimes it is preferable to avoid a 'one out- all out' tripping situation, and there may need to  be more circuits than load estimates alone would require, so that not all of it is lost if there is a fault on one segment. This is especially true if some of the loads are 'dirty' and my cause other loads to suffer from voltage drops( flickering/"brown out") In that case dedicated sockets for expensive computers may be separate from the general ones, if they may be used by the industrial cleaners,  gardeners hedge clippers, or anything that looks like a welding bay ;-)
Note that in a modern building you do not need that many hundred watts per square metre before it starts to heat  uncomfortably,  and offices with lots of kit may actually need cooling rather than heating.
Mike

For an RCBO (or indeed any means of 30mA RCD protection) also consider protective conductor currents - i.e. "earth leakage" in normal use (very common from things with electronic power supplies for example). Generally you'd want to keep normal leakage below about 30% of the RCD's rating (they can validly trip anywhere between 50% and 100% of their nameplate residual rating) - so below 9mA for a 30mA RCD. So if you were supplying say an office full of PCs or the like - which at a rough rule of thumb might leak 1mA each - you might want to limit the number of sockets per circuit to something closer to 9 or 10 rather than 20. Or have a larger circuit without RCD protection and RCDs local to each socket or small groups of sockets (often the case with underfloor bus-bar trunking systems).

   - Andy.

Thank you all for your input, I quite a bit to work with here and I should reach a solution

Wrong question.

The correct question is, how many circuits do I need to create to supply the portable appliances that are expected to be used?