​Talk me out of it please.

Hello, I’m 24m from Belgium and I’m part of a youth theater group (both acting and decor building) and i always had this fantasy of building a giant warehouse with a stage and workshop and a couple smaller rooms if i ever won the lottery or something. Recently i was looking for some metal posts to make a solar panel fence and the metal selling site i was looking at also had a bunch of warehouses for sale and they were cheaper than i expected.

I then started drawing this image for fun to see how big it should approximately be to contain a stage, workshop, storage, offices, living quarters and everything else i would need. This came out at around 22*30*7m and i sent those measurements to a warehouse seller just to get a rough idea of what a well insulated one of that size would cost (160mm walls and 150mm roof) and their answer was 135000€.

The problem is that now it looks borderline feasible. Some quick search i found a empty property of 4000m2 for 190000€. Counting another 100k for the slab and 50k for a basic interior (bathroom, kitchen and bedroom, everything else i would build myself over time)
I would also install a bunch of solar panels and battery’s so it would be basically off-grid.
(The bottom right section on floor 0 and 1 would be private living quarters)

That comes to a total of around 500000€ which considering the current housing market seems like a steal so now I have a kind of brain fart on if this is actually realistic or if I’m just going crazy.

Please talk me out of doing something dumb, thank you.