I would say visit them if possible and try various configurations .
I think you'l find there is not a big difference between the all on one cord 400 and the two cord machines power wise .
So having just two cords can be a neat solution , two vacs and 400 pump on one cord .
The two different heaters ( inline and immersion ) on the other cord on a selectable switch ... ie u cant have both on at same time .. but the immersion can be heating when u are not using the machine .
It may be u like the parallel 6.6 version ( or indeed i think they do a series 6.6 two cord also )
Even if u get this version u could most of the time run it from a good thick single extension cord even if its drawing 15amps or so , but its probably just as easy to access a double socket .
They wont ( id say )do u a four cord machine .
If u get the external steammate , u can run it at the same time as the internal immersion , u would have to run an extension cord to another circuit location in the house though .