1) Yes you do rank up to 8
2) Yes you have to reach 4
3) Yes you will access the Allied quest
4) Yes you will rank up to 8 for the 2.0 tribes

I suppose the reason the Allied rank is 8 for everyone is for synchronization purposes. I assume that the Vanu Vanu will also get that rank soon (after the Gnath and other Beast tribes of Heavensward are introduced)