I hear you. Budget is to follow after scoping. The main thing right now is to figure out the market and ascertain if this is something that requires more investment to get a higher spec van with a longer life, or to start with something more reasonable and test the water.
I lived in a MWB Sprinter for a year, and did a fair bit of work on the interior to tailor it to what we needed. It seems mad that the budget for a weekend van might be 10x the cost of something we lived in full time!
My current thinking is that we either go for a Bongo Friendee style and be content with slightly poky to see how much use it gets, or go all out and get a T5 or T6 and aim to rent it out when not in use.
The main thing is that this doesn't need to act as a car anything other than very occasionally, and primarily it is a camper intended to be comfortable for two people to go climbing, surfing, operate as a base for bike trips and get to remote places for off grid camping.
You're right about not overcomplicating things, in an entire year, including nights at -7c we used our diesel heater once, and I could definitely do without a shower and toilet. Definitely needs to be possible to cook a meal inside comfortably though, both for winter and for being a bit sneaky. I also think people get overly hung up on stealth, and having only used a campsite once in a year, I don't know why people bother.