You will need to re-think your approach. InstantOn is for single site (single subnet) deployments and only 25 APs maximum.
It sounds like you might need Instant APs (different product from InstantOn, terrible naming by Aruba) with Aruba Central cloud management to manage several clusters
Or a controller-based solution using Aruba Mobility Controllers if you really one single control plane for all 6 sites.
If you are forced to use InstantOn because of lack of budget I think you can get away with it as long as you're willing to manage each site as a standalone....I wouldn't like to do that personally.