I wouldn't call them random as some of the ideas he introduces were planned for a while now, it's just he introduces them in a very vague manner. For example the Gaza plan was already familiar to his team: https://www.timesofisrael.com/the-man-with-the-plan-dc-prof-...
I think he introduces these ideas without fully fleshing them either because 1) he's testing the waters to see the public response, and to start a conversation; 2) he may not have all the details anyway and he starts with the first step.
no, he is a corrupt, amoral idiot who is approached all day by hundreds of people and organizations who have all paid in some way to him personally, either financially (like $5M to dine with him at Mar a lago), or via loyalty oaths, or their ability to help him get reelected (Putin) etc. to have his ear on some pet subject. Then they sell him on whatever it is and as his intellect is about on the same par as Homer Simpson, he acts impulsively on it.
It's no different than those local dudes who fall for things like "You can Patent your Invention!" or "You can get Rich with Crypto ! (or Gold! or Coins! or ...)" scams all day. He is both the scammer and the scammed.
His rallies are basically A/B testing of policy ideas. It's how he gets feedback from his base. It works for him because Sr Republican advisors aren't well aligned with the typical Trump voter.
I think he introduces these ideas without fully fleshing them either because 1) he's testing the waters to see the public response, and to start a conversation; 2) he may not have all the details anyway and he starts with the first step.