Our Birchover came with a porta potti - first thing we did was stash it in the garage to gain some storage space as I can't see us ever using it - if we get more into wild camping we can always dig it out. We do have a nice collapsable bucket together with a "bog in a bag" we can carry for emergencies
You are doing the right thing taking time to get the base vehicle right and there are people on here that can give you a lot more advice than me. If doing again I would probably be starting with a T32, to cope with what we carry and tow, and seriously considering 4 Motion. Power wise, I am more than happy with the 150 DSG I have but others swear by the 204 (maybe consider if going for 4 motion?). Trim level, I would stick with Highline as it includes quite a lot of nice extras.
One thing to be aware of with all the convertors you are looking at is that their advertised prices tend be based on the lowest spec vehicles - by the time you start looking at the above together with metallic paint, sat nav, awnings, tow bars, bike racks, solar panels, etc., etc., you can easily bump these up by £10k+. Go armed with an up to date T6 price list and be aware that the convertors will be buying the base vehicles significantly below this (it seems that people haggling are getting discounts of around 12% without trying too hard so I would expect the convertors, buying in larger numbers, to be getting somewhat better deals than this).
Good you are looking at the Californias as well - some people love them, others hate them. Contrary to above though, I think you will struggle to get a similar spec Cali for less than a conversion? I know when I initially did the sums, even allowing for around 12% discount on advertised prices, the Cali was more expensive. That said, I would expect the Cali to retain significantly more of its value if/when you come to sell.
Take your time and don't be pushed into jumping too quickly.
