Sunny,
Your husband should definitely be tested for the Kras mutation before treatment starts. In fact many insurance companies are now requiring it, and it is good for the patient. No sense in getting a drug that won't help you.
Also, you should start getting treated for the rash before you receive treatment (ie this week). Your oncologist should put you on an antibiotic so that hopefully the rash won't develop. I had Erbitux in 2007 and at that time they didn't treat the rash until after it developed. A recent study came out and found that it was much more effective to treat the rash before treatment started. The post about the rash indicating that treatment is working is incorrect. The doctor is going to tell if treatment is working by seeing if the tumor(s) is shrinking and/or the CEA level is declining. I had the rash really bad (I could only complete 10 of 24 treatments) and it didn't work for me.
Jack