You can take a look to Licensing / Layout - HCI Kit Essentials + HCI Kit ROBO Standard for 8 offices ? but that given you a clear answer. I can check later if the named Accel. Kit contains vSAN Lics.
The normal case for a Essentials Plus Customer is the one an only Upgrade Path which is to a vSphere Accelerator Kit Std or Enterprise+ SKU, which upgrade the Bundle into single Licenses and convert the vCenter Essentials to vCenter Std. After that the customer add single licenses to expand the number of Hosts.
Given on the SKU for your HCI Kit "SNS is Required and sold separately. Includes quantity of 1 VMware vSphere 6 Essentials Plus Kit for 3 nodes (Max 2 processors per node) and quantity of 6 VMware vSAN 6 Standard for 1 processor." it might be the same. It looks like that you have to buy VS6-ESP-STD-AK-UG-C or VS6-ESP-EPL-AK-UG-C and than adding normal vSphere ESXi and vSAN CPU based Lics.
Regards,
Joerg
