Not to mention even if you have every lined up you can still get rejected by the co-op board and they don't have to give a reason. They go through all your per

Not to mention even if you have every lined up you can still get rejected by the co-op board and they don't have to give a reason. They go through all your personal details and it's a bit odd living with a bunch of people who know everything about you but you're not able to learn anything about them. 20% down is usually the bottom. A lot of places want 25% or 30% down and there's also a chance you're going against someone with 100% cash and the board will pick them nearly every time. Lastly, if you're using every dime you have so you get a mortgage well over 500k that may be a bad choice. The opportunity cost of tying that much cash up into a mortgage is a lot of risk (all your net worth in 1 investment) and you're unable to use that cash to make other investments and leverage them if need be.