o2 questions?

[ArcticSS]

Cant seem to get rid of these codes since ive had the car. It first had 8 different ones now it has 5 codes. The first code is a p0307 which is a misfire in cylinder 7 which i did not have when i bought the car. That code could prob mean anything. The other codes are p0420 and p0430 with the same codes also pending giving me a total of five. All it says for the last codes is catalyst efficient threshold not met, which i think maybe the cats but im prob wrong. I know the car def needs a tune. Tuning would prob fix some of my problems unless i need new cats. I was told that my car is probably running lean.
The only thing i did was have the rear o2's hooked up and i also changed the drivers side front o2 because it was throwing a no activity code.
Previous owner said he changed plugs and wires when he did the headers late last year.

Was not sure if i should get this fixed before i get it tuned or just have it done while im there.

Don i was going to call you and ask your opinion but i know your a busy guy and would need a few weeks notice. But i would like to set up something in the near future. Wanted to do this sooner but money has been tight. Im only driving the car twice a week. I dont want to damage anything further.