Hello, squib.tandel.
You can upgrade from 7.4 to 8.0 directly. For any significant changes, I recommend checking the release note on 8.0: http://www.cisco.com/c/en/us/td/docs/wireless/controller/release/notes/crn80.html
We recommend going with the latest 8.0 upon transitioning to the new Aironet access points.
Are you already working with your Cisco AM or representative about this requirement?
Let me know if you have additional concerns or e-mail (adawa@cisco.com) me directly. Kind regards.