Then you need cluster license. All other licenses are the same in 7-Mode and C-Mode, but you will need to re-enter them, so make sure to have license code(s) available. You will need to contact your NetApp representative how to obtain cluster license; it makes sense to also ask him about procedure to convert from 7-Mode.
No backup is needed, 7-Mode configuration is not compatible with C-Mode anyway. You will need to completely configure new system from the very beginning.
If you want to switch your system to cdot it is completly disruptive as you will need to reinstall all the dataontap system. About the license you will need a cluster based licence and all protocol ljcense or software are ysing same codes than 7 Mode (8.2+)
About the data: you will need to make a traditional restore to newly created volume (luns or shares) as the 7MTT tool require 2 systems (one 7 Mode and a Cdot as destination)