Help with 05 5.4L first code P0420 then Later P0302
 

Just purchased a used 2005 F150 Lariat for my 19 year old son for a work truck. Has a 130 K miles and is a Texas truck. We live in Georgia. Truck ran great up until couple weeks ago it gave us first a P0420 code. My son continued driving it only short distances while i ordered a Creader VII plus for amazon to help with the diagnostic. Then in the mean time two weeks later we started getting a P0302 misfire, with a Flashing CEL that goes off and on. I got the scanner and it shows misfire cylinder 2. Checking the cat codes shows Cat B1 failed. When idling there is a super strong smell of un-burnt fuel, and at times the exhaust sounds like someone rattling a big tin can. The Cat I'm guessing?

So I have been watching videos and going to tackle changing ALL plugs to SP 546 and then ordered some new coil packs from amazon. Then will tackle the Cat issue.
So my questions:
+ Could the misfire had been happening for a while? Then causing the Cat to go bad? or could it happen possibly in reverse condition?
+ After a plug and coil pack change, I'm guessing I most likely will still have the Cat code? Can it damage the engine running with the clogged Cat?
+ I have seen others cutting open the Cat and welding it up to buy some time. Would this damage the engine to do so? Would it pass emissions if I welded it up empty?
Just trying to fix this truck and figure out if its worth keeping before dumping a lot of money into fixing the Cat.
Thanks for an help