They haven't really gone with any particular era from the comics. I understand your concerns regarding Mystique. She isn't even close to the character from the comics, or the Rebecca Romjin version.
It looks like the lineup is Jean Grey, Cyclops, Beast, Mystique, Nightcrawler, Quicksilver, Havok and Jubilee. Of course, we've seen that there will be a Wolverine cameo, but that could be very brief.
The choices for the Four Horsemen are a change. Of the four, I believe only Angel/Archangel has been a horseman in the comics. Magneto and Storm were horsemen in one of the X-Men cartoons (Evolution), but never the books. Psylocke is the fourth, though IMDB also lists actors or actresses for Death and Plague. Death and Pestilence have been names Apocalypse gave to horsemen in the books. Archangel, Wolverine and Gambit have all been converted into his Death at one time or another.
There are also Morlocks, including Caliban, in the cast list.