We have a 220 it has plenty of power.. if you plan on towing a lot then you should really get one with a factory fit tow bar and a 250 would make that much easier. But I have no doubts that a 220 would cope. I believe the factory fit tow bar has several upgraded radiators to assist with cooling the engine and the gearbox so this should be considered.
We have a Horizon, it has doors on both sides, 2 kids and it has child locks but we don’t use them since they can’t reach the door handles when seated and besides that the kids almost instantly identified the open/close buttons on the door pillar, they are not disabled with the child locks.. rendering the child locks sort of pointless.
The horizon is ideal for us since it’s our only car and we couldn’t really justify the kitchenette, consequently we can sleep 5 and have 2 rear doors. We don’t have a night heater, just a decent duvet. We recently came back from a mild wet week in Scotland and had no issues with keeping warm. I don’t think we will need a heater,
Heater/250 nice but not essential.
We will be buying a mattress topper those seats are not the most comfortable..