I've put together a confirmed list of ways to earn Ghost Clan XP on my clan's website. Will keep it updated to the very latest Intel! Hope this helps!
I've found it's much simpler than that for multiplayer modes. 50 Clan XP per Member per Win. 10 Clan XP per Member per Loss. Not sure Clan vs. Clan or about Clan Wars yet. Will update my clan website FAQ as soon as details are confirmed. I'm also keeping an updated list of confirmed Rewards for each Clan Level!