Wow thanks for the responses, all very helpful.
I've checked comparison websites online, that's about it. I don't see why we shouldn't, I should have a fine credit rating from paying off my car finance, other than that no debts.
Not sure where I got the BSS cost from but I've seen one site mention it as being £160 every 4 years.
I prefer the idea of compost toilets, not sure I like the idea of carrying around your own raw sewage for many months (heard too many stories of leaks etc).
The electric costs were meant to factor in the months where solar wouldn't be viable, this may need to be higher.
I've adjusted some prices to be more inline your estimates. The paint job was based off multiple online sources, £100/ft every 3 years is what I've constantly seen, but maybe I'll increase this to every 5 years and just touch up the odd place here and there - we'd like to keep it looking pretty fresh. Where did you get your insurance from? I just got a random quote (can't remember where from) but that was including household items. Other maintenance is just a buffer zone for unexpected costs, don't wanna get caught out by the odd leak here etc.
Were you a continuous cruiser? I've increased to £1000 to err on the side of caution.
In terms of internet usage we'll using quite heavily as my job relies on it (software developer) and this is what we've seen from EE for 100gb a month I believe.
I've factored in all your suggestions guys, very much appreciate the help.