HELP - - CEL here are the codes
 

[&:]I have this car that I purchased back in February and the dealer sold it to me for $12,500.00 I knew the guy but my 00 A6 also had the ABS light on - - The dealer did fix it cost them $1,280.00, he was NOT happy about that after selling me the car for under $13,000. The car did have 71,000 miles on it when I bought it but I asked around and was told that this was still a steal so I should go for it, and I did.
While I love the drive of the car there are things that are driving me [:o] bonkers.
I took it to a place that checks ur car for free and these are the codes he gave me. HELP!
17087 - brake light switch - F, electrical problem in circuit (P0703) error occurs intermittent
16955 brake light sweitch -F no a plausible signal (P0571) error occurs intermittent

16805 warm up catalyst efficiency (bank 1) below limit (P0421)
16815 warm up catalyst efficiency (bank 2) below limit (P0431)

HELP!!!!!!![:o] HELP!!!!!!!
How serious r these things and should I sell this car? Or get these things fixed?
Are these repairs that I can do myself or another shop or should I take it to the dealer?

Thanks a bunch for ur thoughts and expertise!