Ohad is speaking about InstantAP version = iAP-205
In a single cluster there can be up to 2000 devices with the lastest firmware as far i know. Is not a hard limit but is recommended.
Just in AP 9x model the cluster is limited to 254 devices per cluster, but your AP is a 225 so you should be good to go!, you got the AP with the best CPU RAM of all Aruba APs.
- How many Instants APS you can connect together?
There is no limit as such, but the number of IAPs in that Instant network, managed by a single virtual controller, depends on the RF and also the client density.