1998 Honda Civic Engine misfire after radiator replacement

Only trouble code was random misfire. Did a test on it yesterday, turned out it was a bad spark plug. Changed the plugs, now it will start but immediately dies after accelerator is released. Going to change wires next but have to wait until weekend to get some money.

Dang, I guess I'd better be completely honest. So I tested the plugs tonight, found it was the #2 plug that was bad. So I DROVE the car (keep in mind it's running on 3 cylinders at this point) to the local auto parts store (less than 1 mile away), it is in "limp-home-mode" meaning it tries to die when there is no pressure on accelerator. Got it home, waited about 40 minutes to cool, then replaced plugs. Wires don't look so good but were still working. Now it will barely start, only if I give it gas will it run, as soon as there is no gas the engine dies. NO white smoke, all sensors are tight, when I give it gas when it's running the engine sounds normal above 2000rpm. When I initially removed the plugs there was no coolant smell and only a slight gas smell on what turned out to be the bad plug (understandable if misfire). Any ideas on this one? I know I was an extreme stupid to drive it but have no friendly neighbors and husband works graveyard.

I replaced the spark plug wires tonight, engine is no longer missing and CEL is not flashing anymore. Engine sounds great! Only problem now is it wants to overheat. I test drove it about 3 miles, during drive temp gauge goes up and down but doesn't hit the red zone. When I got home and let it idle, the temp gauge went almost to red but still no CEL. I did not hear the thermostat open at idle either. The fans (both radiator and engine) both operate. The coolant in the reservoir looks light, after all the stuff I've done should I drain and refill and see if that helps? Or should I remove the thermostat and test it? Installed a new one when I installed new radiator and hoses.

Checked again, found that the coolant was low. Added more (I don't think at this point it is a head gasket leak as there are no leaks present and no steam or smoke) and took it for a test drive, both city driving and about 2 miles on the freeway. Thermostat opened, temp gauge stayed at below halfpoint, no hesitation or missing, no CEL. Let it idle for about 5 minutes after returning home and gauge still didn't move above normal. I have my fingers tightly crossed that it is now fixed. I will be changing the fuel filter this weekend to complete a very scary tuneup job. Thanks for all your help!

Thought I did. Anyway, drove it today and on the way home CEL came on again, not flashing. Engine still running fine. Took it to O'Reilly's, OBD scan pulled P0420 (catalyst system efficiency below threshold). I don't have the tools to check the TWC, will driving it harm the engine? I know it won't pass emissions (don't have to do that til next year) but I don't want to replace it just yet. Thanks, you guys are the best!