Only the Primary SonicWall needs to be configured (in some cases you may need to log in to the Backup appliance and turn off the PortShielding feature).
The Primary SonicWall is the only appliance that needs to have the Security Services Licenses on.
When the appliances have been registered correctly in the same MySonicWall account they will share the licenses across both appliances.
All settings and licensing are synchronised across both Appliances.
Cost for 1 SonicWALL Stateful High Availability license for an NSA 3600 is about $800.00