I think that if you chop a block into six slices, that it is a convenient size, divisible by your two colonies and potentially saves waste.
A handy idea for storage and serving, is in empty 1 litre juice cartons. Make a cut at the top, side and bottom to produce a box with a lid flap. The fondant will flow over time in storage and so will be restrained conveniently by the box until you need it. A bit of tape, elastic band, string or what-have-you will keep the boxes closed while on the shelf.
If vertical space is restricted slice it long ways (gets to be a bit more of a struggle) and wrap in cling film. Slash the film before putting on a crown board or top bars. Placed on the top bars, if there is too much and the bees don't eat it, it will flow between the bars and be a right royal pain to remove in the spring.