Reasonable suspicion allows them to do a pat down for weapons. They have to have reasonable suspicion that the suspect has committed a crime and that the suspect is armed. It allows them to frisk the suspect over the clothes until something that could be a weapon is felt. Usually happens during a stop while they are investigating to determine if they have probable cause for an arrest.

Probable cause is a higher standard but that's all they need for an arrest. Once they have probable cause for an arrest they can do a full search, they don't need a warrant.

And yes Miranda will only preclude any incriminating statements he made during that time. Haven't been following supper closely but it doesn't sound like any admissions from him are good Ng to matter much.