Sort off yes. You will also be able to live under-water.
The stages are to be Microbe, Multicellular, Aware, Awakening, Society, Industrial, and at last the space stage. Multicellular through Awakening are sort off like the creature stages.
There will also be creatures of varying sizes, yes, albeit the won't be the specific "epic" prefix for giant version creatures.
Currently there are no plans for real multiplayer. Although that might be changed in the future, or added as a mod, since the game is going to be highly mod-able.