For ZD high availability, you buy two controllers and configure smart redundancy. Each controller comes with 5 AP licenses and when you configure smart redundancy, the licenses pool (each controller licensed for 10). If you have a total of 50 APs then you need to buy 40 more licenses.
901-1205-UN00 - ZD1200 Controller (you need 2)
909-0001-ZD12 - AP license for 1 AP (you need 40)
Support is optional but recommended:
801-1205-1000 - support for the first ZD (you need 1)
803-1200-1RDY - support for the second ZD (you need 1)
801-1201-1L00 - support for AP licenses (you need 40)