Few questions regarding my 94 prizm

[JustinGB]

Not too long ago i was driving on a road under construction that was being resurfaced. While i was driving, since the road was being resurfaced, all the manholes and gas pipelines were exposed and not flush with the ground. Long story short is my resonator took a shot from the gas pipe and have had a huge exhaust leak.
I've fixed the resonator by removing it and just welding in a new pipe, then i discovered another leak. On the front of the engine where it connects to the exhaust manifold. From the stress the hit took it stripped one of the holes on the engine that you screw the manifodl to. Fortunately just one.
How hard would it be to retap the hole? Would it be the same process as tapping anything?
Also, i'll be replacing my cat because it's got 140k worth of crap and I bet it would restore some of the stock power in my car. When I rework the exhaust, is it necessary to have that sealant goo exhaust shops use on the gaskets?
I bought a few things, for the exhaust, mainly this aftermarket header because i got it for an extraordinally good price and a high flow cat. Hopefully everything bolts on and all the corolla 93-97 exhaust systems are the same. It should be since it's a 4afe toyota.

last but not least, are the breaks for same year corollas the same for prizms? front and back? I need new rotors/calipers/brakes and rear break items aswell

THank you very much, i've beenr eading on this forum this whole week and learned lots of o thigns! thanks a lot

[Nutter]

Regarding the stripped hole for your exhaust manifold, I'd probably recommend a Heli-Coil. It is a fantastic way to repair something like that, and its really not terribly difficult to do. These are readily available in a variety of sizes at most auto parts stores. You can buy a kit that has everything you need for the application you're using it on. HTH.