Hi Lizzy, I see you're in London, so I may be assuming, so if I am and I've got it wrong, I apologise. But if you're planning to cruise around the capital, run a fridge off solar and cruise only every 14 days, then 500 or 600w might be a better idea. Yes there are a lot of ccers on this board but they would probably have more engine running time than a London ccer, probably moving a lot more often and that can make your needs quite different.
We've got a fridge (Shoreline 12V) with an ice box, the ice box is plenty big enough for our needs. I'd question the wisdom of having a separate freezer, the only people I know who cruise who have them have very sophisticated electrical systems with onboard gensets etc. Most cruisers I know, don't even have a fridge.
Also as Mike says, Webastos and Ebers require batteries in good condition. If you're new to boating it can take a while to get used to living onboard and the electric systems and batteries are often the first things to suffer. Agree with getting a burner fitted, swap lights for LED, but personally I'd go for a 12v fridge over one with an inverter, I'm of the keep it simple school of thought and inverters are just one more thing that can go wrong.