@MartinLL's answer covers most needed. I would also like to point out that there are two licensing models of interest. - Co-term licensing: where every license you buy terminates on the same date, even if you add devices with licenses later on. - Subscription licensing: where you simpler SKU especially if you are using other gear like switches and MX firewall appliances and where you can choose to pay automatically per period for your licenses or have a set period with pre paid licenses. Other than that you choose your hardware according to the needs of the customer and 1 device = 1 license. License tiers are enterprise and advanced in the co-term model or essentials and advantage in the subscription model.  The higher tier provices umbrella integration (DNS security), adaptive policy (segmentation via tags instead of VLANs, advanced wireless stuff like AI RRM and full blown intelligent capture). The license SKU's usually come in 1, 3, 5, 7 and 10 year options. ... View more