P0446 P1124 P1126 CEL Lights

[HELLAS59]

Hello Everyone.

I have a 1999 Boxster Tiptronic Base Model with the codes mentioned in the title. I am not very Mech Savvy which is why I am asking for you good folks to give me some guidance on these problems. I recently took the car to a nearby mechanic and he told me that I need to replace the Catalytic Converter (I ve had a really loud rattle for some time now) as well as a crank sensor that I am not familiar with. I guess my question is: can these codes P0446 P1124 P1126 be caused by the problems mentioned by my mechanic? Ive read that those codes most likely indicate an Air Leak, a bad AOS, dirty fuel injectors, and a few other reasons. I was quoted a bill of over $1700 to fix both problems. And if my Cat is rattling, does it necessarily mean that I need to replace the whole thing? If so, I have read online that the best route would be to buy used OEM. Any feedback/help would be greatly appreciated my brothers.