Jaggernaut

Hey Guys and Gals,
I've been having some problems with my 2000 Lexus ES300 lately. I have noticed some sluggish throttle response times, a metal rattling (sounds like metal on metal) but only when accelerating in gear, sounds fine when it's in park, and also my headlight indicator on my instrument panel no longer lights up when the headlights are on. I ran the car on my OBD-II reader and it spit out the following codes
P0100 - MAF or VAF A Circuit Malfunction
P0110 - IAT Sensor Malfunction
P0330 - Knock Sensor 2 Circuit Malfunction (Bank 2)
P0420 - Catalyst Efficiency Below Threshold (Bank 1)

My first question would be which problem should I get fixed first? I.E if something could be causing damage to make the other codes spit out. Don't want to spend money on a new Cat if the IAT is messing with it. you know? Why pay for the same part twice. Also, I just replaced the MAF sensor roughly 6 months ago because it somehow got cracked so the actual sensor wasn't connected.
Secondly, Would anyone know of a website where I can look up the OEM parts numbers for different parts in my Lexus? This would be extremely helpful and not waste time posting these questions on here. Could be a sticky too??? I don't know.
Thirdly, could the catalyst code be sending out a false reading for the knock code? And since I replaced the MAF sensor, should I unplug the battery to help the ECU relearn said sensor? If so, how long would be adequate?
Lastly, I have checked my manual and have yet to come to a conclusion on where Bank 2 is for the P0330 code and where Bank 1 is for the P0420 code.

Thank anyone for any advice that they can give me. If you need any more info, just ask!