Answer the questions your patients or clients already ask you. The best expert content is the explanation you give in consultations, said once to a camera. You never run out of material because your daily work is the content pipeline.
Stop reading and start explaining. Know your points, not your exact words, talk to one person instead of an audience, and do several relaxed takes. Stiffness comes from trying to recite a script perfectly; naturalness comes from speaking the way you already do in the room.
No. A recent phone, good light, and clear audio outperform expensive gear used badly. What makes video look professional is framing, lighting, and sound, not the price of the camera. Start with what you have and upgrade only when a real limit appears.
One to three good videos a week, filmed in a single batch. For a busy expert, consistency over months beats volume in bursts. Batching all your recording into one short session makes a sustainable pace realistic without eating your week.