coolant and go. Once the hose came off you needed to bleed the system to get out any air pockets. Since you didn't, when you added coolant, there were local hot spots which allowed the coolant to boil and the engine to overheat.
You may or may not have blown the head gaskets but I would fix the ignition issue, top off the coolant and start it. Bleed the system and then look for signs of water in the oil or oil in the coolant as suggested. To be sure run a compression test once it is warm.