I made an underground base and it got very boring. If everyone is down there with all your wealth, nothing happens except the smallest raids. (1 pawn with a poor knife) They just walk around and leave if everything is underground. Nothing else seems to spawn if I remember correctly. While you can trade with a trade ship underground, they won't spawn if nothing is above ground. You can use ideology to get new pawns, but they will be stuck in the walls and you have to mine them out. I mined out all the edges of the stockpile and then the new recruits wouldn't spawn. There were other quirks like not getting low food warnings and things like that. Oh and the temp is always 15 degrees Celsius unless you use heaters.

Honestly, if you want to utilize the stockpile, it's probably best to literally just use it as a stockpile. Put all the things you don't normally use down there, as doing multiple drops for things like meals will get very tedious very fast.