you should be able to answer all of your questions right here.
I have read almost every thing in these sections of idaho law an as my interpretation goes you are not required to even inform police officers if you are armed when you are pulled over. If you are open carrying however, unless you have a CCP, the weapon must be in plain sight, which would tell him you were armed any way. Further more you are not even required to provide ID or submit to a Terry search if approached by an officer while you go about your business. of course you may choose to, but take into account the story of your friend above, many officers are ignorant of the law.
Also, according to article 1 section 11 of the Idaho constitution i believe that it was illegal for the officers to confiscate his ammunition. it certainly was for them to disarm him, however, I don't believe they violated the confiscation clause as it was returned to him, albeit in a very fearful manner.