Without knowing where it will be you can't know what size of supply is available, or the earthing and binding arrangements required.
This will likely need a 63A supply with that big water heater in it, but until you know where it is going you won't know how much capacity is available for it.
What is the unit constructed from, is there any metalwork? Is it a metal structure. Being road legal it presumably is built on some kind of trailer base, with wheels and stabilising legs? In which case for some types of electricity supply it will need to have its own earthing system created by the installation of earth rods as it could be dangerous to use the installations earth, for other types of supply it will be fine to use the installations earth.
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Ceeform connectors are available in 16A,32A,63A and 125A
You will 'get away with' a consumer unit which has enough ways to serve all of the circuits you have. As far as I can see you have 5 or possibly 6 circuits so a 6 way CU will probably suffice (I can't see much need for spare ways in this application)
As for the physical size you'll just have to read datasheets to see how big they are, although choosing the smallest one will make it more awkward to work on.
You need to decide which circuits require RCD protection based on what they are doing and how they are installed.
If you are connecting it via a Ceeform plug it will use a trailing lead made from flexible cable to connect it, not an SWA. SWA is not suitable for making trailing leads.
