Handgunlaw.us is a good place to check out. As for MN, the "No guns allowed on the premises" signs do not carry the force of law. You may carry past the signs legally. To get into any trouble, you must refuse to leave after being asked to do so by the property owner/tenant.
I don't have any experience with IA--I've only driven through it.
+1 on 00 Buck's recommendation. Outside of that I do think it behooves you to ALWAYS inform LEO. It can't hurt and in my experience (yes, I am a lead foot) has more often led to a friendly warning vice citation.
I disagree. If in a "not required to inform" state, I would only inform a LEO if they would actually see/find the firearm. Example: asked to step out of a vehicle and cover garment might have ridden up or something. When talking with a LEO, the safest place for my pistol is in its holster. If you inform, the best case scenario is the officer just asks you to leave it in the holster. Sometimes this is not the case and the officer disarms you and unloads your pistol. Traffic stops can be high-stress environments, especially for LEO since they never know what they'll find in a car. Introducing an unfamiliar firearm for the LEO to handle at a potentially stressful time doesn't seem like a great idea to me.
If you inform when not required to (within reason), it's kind of like playing the lottery. Sure, you might get off with a warning, but a multitude of other bad things could happen.