I don't believe there is a requirement to start CoP (could be wrong) but I can tell you how many times I've been in a party in Qufim when someone says 'Lets go kill gobs in the tower' then we have to wait for 15 minutes while someone in the party watches the 1st CoP scene. Zillart missions start after obtaining rank 6 (defeating the Shadowlord) and you have to get up to ZM14 to have Sky access and CoP Mission 7-5 to get Sea access. The Zillart missions require a fairly high level (65+ for most of them) to complete, but CoP starts you at 30 capped missions. Not that CoP is 'easier' than Zilart, quite the opposite acctually. Me and some friends did Zillart from 0 -> Sky in about a week. After 2 years, I'm still on the damn Mamet fight in CoP ><