Hi
yes you can have 1 wlc as secondary if both ha members fails.
You can use the mobility configuration group.
For licenses, I don't remember as I'm not an expert in sales but at least you should have enough AP licenses to hosts all your APs
You can have a look on this document page 45:
http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-5/High_Availability_DG.pdf
Thanks
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Thanks
Francesco
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