A guest told me yesterday that she read on a website that MK capacity is "650,000" LOL! ... While I can not give the actual number, it is considerably less than that.
Phase 3 means resort guests and AP/PAP only. If you are staying at a resort, you can get in... I don't know how else to say that...
Phase 4 is complete closure. Each of the parks has its own capacity and will close independently of the others.
*Edit*
MK Phase 2 @ 10am. Probably approaching 3.