OBDII Codes P0300 and P0430 on Nissan Sentra GXE

Having a problem with my 2002 Nissan Sentra GXE. My Check Engine Light has been on for quite a while. Financial situations did not allow for any repairs at the time. However my car has been starting without any problems or any decrease in power. Recently it has been starting with some difficulty. What I mean by this is that it starts on the first try, but seems to struggle to stay on, then after about one minute, the idle smoothes out. Now, for the first time, it did not start. The engine turns, but does not start. I purchased an OBDII scanner and the codes I get are P0300, Cylinder Misfire Detected, and P0430, Catalyst System Efficiency Below Threshold (Bank 2). Can anyone tell me what I should be looking for to replace? What should I be troubleshooting? Any help is greatly appreciated. Thanks!

When was the last time a tune up was performed?

Make sure you use good quality parts and plugs that the engine calls for.

If the CEL has been on for "quite a while", it's possible the misfires has damaged the cat on Bank 2 and may have to be replaced as well.

Will your scanner monitor engine temp, open/closed loop, O2 activity?

Good luck and keep us posted.