Starting over from scratch is a little extreme. All he has to do is pick his favorites and keep them. None of those fish are incompatible.
I don't think you should trade any fish, just get rid of many of the ones you have. If you drop your stock to UNDER an acceptable level, then you should wait, get used to the fish, and then consider getting something different. Since you can't take care of what you have now, thinking of new fish under any circumstances is a bad idea.
Garlic helps boost immune systems in fish, but will not kill Ich.