Do you think that all happened because of the dealer putting too much oil in the car?

Overfilling the crankcase could not have affected the ignition system. If it is a failed coil pack, it is coincidental.

If he is still running that ruined catalytic converter, that could be at the root of the problem. Burning off that much oil could have made that cat get really hot, enough to melt the innards and cause partial intermittant blockage of the exhaust.

tanstaafl.