Your post brought back so many memories. The story of this BX is so close to mine that it made me smile.
Back in 2019, my brother's friend's father bought an old farm and in the barn was this old BX.The friend's father offered that BX to my brother as he was in to Citroens, but my brother wasn't interested. He mentioned it to me and my interest went away when I heard it was a van. A few months passed and then my brother mentioned it again and said that it would be scrapped. I decided to at least have a look at it as it was going to be scrapped anyway.

It had 179k on the clock, almost no rust and seemed very tidy. I came back with battery and fuel and guess what, it started as if it had been left there yesterday. I bought it for 120€ and it came with a crashed spare car.

I kidd you not, I drove the thing to my place (only 10km).
The last time it was MOT'd was in 2005 and it also had a notification for smoking (valve stem seals). Even though it was in good condition, I did a lot of work on it and spent about 1000€ on repairs, but I think it was worth it. It still makes me laugh when I drive it in the summer, not because I enjoy it (although I do), but because so many people laugh at me and how hideous the car looks.
Sorry for the off-topic, but I felt I had to share this story. Vans are not worth much. Personally, I would not pay more than a couple of hundred quid for a project like that. The reason is simple: because nobody wants them and you might be able to sell one in good condition for 1000-2000€ on a good day. That's the main reason I still have mine, because no one wants it and I'm afraid no one will take good care of it because it's just a van.
If you need any help or advice, you can hit me up!