There are probably a couple “module size sweetspots” among those:
1)car transport size – crane free (represented by a cube model)
2) Bed pot size (represented by the sleeping box below)
3) Container size (represented by a standard mobil home)
4) house size (represented by the concrete float coast guard base in ecuador with a 3 floor house on top)
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Each of those sizes has his own advantage/disadvantage spectum my favorite is the smallest one as you can always build the bigger modules assembling smaller modules – but not reverse – so the smaller the module the more flexible the concept.
For example you can easyly raft up “car transport modules” to a container size platform…as you see me doing in the picture below.
So you would have “sub modules” connected to a “living space unit” of room size – connected to a house – connected to….