This was answered in the discord, but reposting here to so anyone who comes across it has the same questions.
Currently there’s no way to stop paying upkeep for a room, but the next version will probably have a way to deconstruct rooms you don’t want anymore.
Corruption sources
There’s a few different ways. The most immediate is studying forbidden tomes. Standing near large crystals, studying crystal items, or standing in pockets of corruption at tower ruins, gives you contamination which builds up to corruption as well.
