1. Is it possible to use R600 Unleshed APs in my existing ZoneDirector 1100 setup?
An unleashed R600 will not join to a ZD, however a regular ZD1100 will allow control of a R600 and supports firmware up to 9.9, this will require an additional license on the ZD. The ZD1100 is EoL controller and the ZD1200 is the direct replacement.
2. The ZD has a license for only 6APs. I assume that this will not change when I add R600 Unleashed APs? R600 APs support up to 25 APs.
No this will not change
3. Can a R600 Unleashed AP handle 7982 APs ?
No. Ruckus unleashed only supports R500 and R600 access points
4. Does it make more sense to kick out the ZD 1100 and setup a new WLAN network based on R600 Unleashed?
For you yes, but you would not be able to manage your 7982s under the same pane of glass.
5. Is there any benefit of running a ZD 1100 with regards to functionaliyt compared to a R600 Unleashed network? I don't plan to have more than 10 APs in my network.
Unleashed is designed for a simple network. Access points are on the same broadcast domain. WLAN and access point groups are not supported and at present meshing is not supported either. External authentication, guest ports are supported. If you'll have less than 10 access points at a single location and you do not use WLAN groups/ AP groups then unleashed could work for you.