Advise on part-time camper

Hi,
I am looking into buying my first van that I would like to use as a camper during the warm season and at the beginning to use it only within UK, no travels to continental Europe yet.
However my other objective is to use it as a van to also transport some bulkier things if I need to (NOT TO use it as a removal van).
e.g. if I need new doors to my house I have to hire a van. Things like that. A lot of custom built campervans have the back blocked.
Currently I drive a standard car to what I can fit a bicycle if I take the front wheel off so not much.
Anything that is over 2m long won’t fit.
I think this van is going to replace the current car so as you can imagine I don’t want to jump straight into a big van e.g. Mercedes Sprinter to go shopping for instance.
It’s not that I worry about driving a big van. I actually drove much bigger vans and quite enjoy it. I think the visibility in a van is way better than in a standard car and even if the vehicle is longer and wider the maneuvering is quite easy.

I am looking into these newish Volkswagens (Transporter, Caravelle) and Fords (Transit Custom) for instance. I think Caravelle looks good but it could be it’s a bit too small. Perhaps Transits, Vauxhall Vivaro or similar are a bit bigger.
Ready campervans are more expensive than the standard vans but what I see there are significant differences.
e.g. seats, air conditioning, pop up roof.
I am worried that if jump into buying a standard van (e.g. some white ones) used by the companies I will miss some of the important features that will make my life on the road easier and more comfortable.
However e.g. Executive range of VW Caravelle does come at a price.

I want to meet somewhere in the middle between regular van and high end van and I don’t need it to be built for 247 living in it.
I can see some of them have the rear seats reclining which can be used for sleeping.
And I would appreciate a van that have more windows so on the sides and at the back.
I can add and remove things at the back as my journey with vans/campervans progresses but initially pretty much empty except some seats.

I am in the process of writing down a list of things to pay attention to when fishing for a van.
e.g. 6-gear manual, diesel, air-conditioning, cruise control. I think things like rear view/reversing camera is good.
Things like engine models, reliability, blue motion good or bad?

Alternatively I could buy something like a big family van (with windows) and slowly convert it into a camper.
I have no experience but perhaps start by upgrading the front seats.

As you can see my mind has created a dilemma I now have a difficulty reconciling.
I am sure I am overthinking it but it’s because I very rarely change cars (quite loyal to them) and not in a habit of buying then to sell it next year.

What do you think? What should I pay attention to?