Devil can not only read hearts and minds, but write in them, too. This is reflected in the usage "and he put... in his heart". Reading most minds, however, is an incredibly boring proposition. So is writing in them, too - if one is to look at protocols of the witches' processes, then what was the devil putting in them?- mostly the things like drying the milk in the neighbor's cow, sophomoric pranks about making some girl's ex-boyfriend impotent, settling minor scores about regular quarrels in their small villages and other things of similar sophistication. From the devil one would expect more. Imagine having to write [on purpose] at the level of 5-year old. It is boring.
I'm with you on the "put...in his heart" comment. I believe that is what I was trying to say by "throwing thoughts into our minds". But I'm not so sure about the "reading" part. I'm no expert on this, and I'm not trying to be combative with you. But this goes against things that I've heard, and read in the past. I'd be interested to see if there is official Catholic teaching on this.
No. Demons can see sin, and when one sins, one leaves oneself open to temptation. Demons will use sin against an exorcist or anyone at an exorcism, but they don't know what the person is thinking. This is why everyone at an exorcism has the Sacrament of Penance beforehand. Don't give the demons any weapons.
Remember, demons are not God, they are powers and principalities, mostly. Fallen angels. They chose that path and they want to take anyone they can with them, so they deceive and taunt and tempt until a good person gives in to evil.