1998 Chevy Camaro

Hi! I have a 1998 Chevy Camaro, V6 3.8- 88,000 miles. I just yesterday had my crankshaft sensor replaced in the car. I had been experiencing stalling at red lights, stop signs, ect. I also was experiencing stalling while actually driving the car. My service engine light had been on for awhile, and everytime the car stalled, my "check gages" light then would come on. The car would start right back up after it stalled out though. Weird? Never have really had a ny trouble starting it. The mechanic said yester though, that this was happening due to a non-functional crankshaft sensor. Not really sure what this does? I paid 165.00 though to have that replaced. I also have a bad catalytic converter. No smells are coming from it, just a horrible rattling noise. I have a few questions. First, does replacing the crankshaft sensor sound correct for the symptoms I was experiencing with the car? Also, did I pay too much to have the work done? Second, the mechanic has said my car may keep stalling until I replace the catalytic converter. Is that correct? I have been told for my particular camaro- engine size- 3.8 V6, and year 1998, that I need a direct fit converter that has to be a manufacturer converter (chevy) which I have been quoted by several different repair shops around 800.00 for the part alone! Does this sound right? As long as I have a direct fit converter, that should do the job right? My service engine light is off right now, as it has been reset yesterday during the crankshift sensor change. The mechanic said it will probably come back on because of the catalytic converter. Does this sound right. Or is the mechanic just saying this to make a quick 165.00 off of me yesterday to have the sensor replaced when it may have not even needed it? Sorry about all the?'S I just want to try to understand things better for I pay too much for things to be done. Any help is very much appreciated. Thank you! ~ :)