1. What? You obviously want a hand that plays good multiway in this spot like Suited connectors and pocket pairs. Basically you want pot odds
in your favor, if it is going multi way against 3 short stacks with 30BB each just fold, but if everyone is 100BB deep you can call wider.
2. I treat it like the CO, it is not a good idea to flat from the CO because you are basically hoping the button folds or that you flop a good hand. Flatting in the cut off opens you up to squeezes and puts you at a chance of being OOP during the hand.
3. We should never be 30bb deep in a cash game and if for some crazy reason we are why would we play KTs? If I was 30bb deep I would never flat in late position because a shove is much more effective.