Do all orthodontists take molds of your teeth? is it necessary?

Yes. yes.: Yes. All orthodontists use dental models. And are necessary for diagnosis/treatment.

Yes: Either actual molds or electronic virtual molds. That way the Orthodontist can see your teeth outside as sell as inside, determine size and positional relationships, compare too size to supporting bone size, and better plan your treatment. Asking the Orthodontist to diagnose and treatment plan you is liking asking the Cardiologist to Rx you without benefit of an EKG.

Yes and yes: The orthodontist needs to be able to study your bite and the positions of all of your teeth from different angles. Without molds (impression and study casts) they can't tell how your teeth fit together from the inside of your mouth