2006 nissan maxima

so Yah ive been driving for 2 years with a bad catlytic converter and my engine had been leaking oil so at 188oooKms its time for a new engine. I'm pretty pissed yah but i cant be pissed at my own irresponsibility.

So one day my engine starts making a really bad gridning/knocking noise everytime i start my car and i'm afraid to drive it, so my mechanic told me it had to do something about a part that only Nissan offers for about 1600 and told me might aswell buy a new engine instead of replacing that part that has to do something with the oil pan or something.

either way i found another person out of province that said he would do the work for $2000, including the engine and labor with 136oookms .

I was wondering if its a good idea to replace the catalytic converter aswell when i do my work for the engine? the only problem for me is finding the catlytic converter (cheap aftermarket most likely) and sending it down to the guy who is installing my engine. And also do you guys think i is also a wise idea to replace the used timing chain tensioner with another new timing chain tensioner while the motor is already pulled out of the junkyard?

thanks for any opinions and replies before hand cheers