Can I get a 3 zone split 0utside heat pump unit and purchase inside handlers one at a time?

Expandability is a great feature of multi-zone mini splits, however, all multizone mini splits of any brand require minimum two air handlers being attached in order to function.  Other than that, the only consideration is that you purchase an outdoor unit with enough capacity and enough connections to accommodate all the air handlers you will eventually attach. If you have any further questions or need further assistance, please feel free to reach out to one of our experienced customer service representatives and they would be happy to assist you. Thank you and have a wonderful day.