There are one or two warning lights on the dashboard that mean "drive carefully until you can get it repaired", but the over temp light and the oil light especially mean "stop now or you'll wreck the engine--really we mean it, stop right now." It's too bad more people don't understand this.
"possible exhaust system leak or damaged catalytic converter" sounds like they have not done a proper diagnosis, only read the codes. They might want to charge you more shop time for a proper diagnosis. But since the car is driveable, you also don't have to have the work done at a dealership and you can probably get a better price at an independent shop.
This is what I would do: First, get a proper diagnosis; a leaky exhaust system should be a cheap fix and would not be unexpected on a 7 year old car. If it is a bad catalytic converter, don't get it done right away. When you overheated the engine, you might have damaged it beyond usefulness. If this is the case, you may start burning oil excessively or leaking coolant into the engine block. Drive the car for a few weeks, checking the oil and coolant at least once a week. Pay special attention to any foaming in the oil or at the radiator cap. If you start burning oil or loosing coolant on a regular basis, you either need a major overhaul or to ditch the car entirely, so you should probably avoid paying for the converter until you know for sure. On the other hand, if you are not burning oil or coolant, then you may have dodged a bullet, and replacing the converter will get you a few more years.