Hi Milan,
i have Lagoon 420, 2009 and I live in Australia, Passing Townsville as we speak. I can voice a few suggestions with what I have learnt to date.
if you are keeping the boat in Aus change over to 240. Put in 800watts plus of quality solar, rainmaker desal in 240v and 12v with 100litre plus per hour, your inverter is good and house capacity too, Victron inverters are good. If you can pass on where you are I might be able to pass on a reliable contractor which is hard to find at times.
cheers
simon
