All those class titles sound promising! Maybe in order to have the Cerberus side have the same exact number of classes as the Systems Alliance, you could have a version of a Guardian. Custom animations might not even be necessary. You could have the unit's block animation be the stock crouch animation, so when it moved while blocking it would also be in a more defensive position. I also guess the combo file would need to be edited so there would only be one position for blocking, and the shield shouldn't be able to block biotic abilities and...
Anyway, that is just my idea.
All the concept units for the Reaper side sound good. I think it will match the Systems Alliance side well. Is there any chance that different sides will fight each other? I think it would be difficult to work in and still be canonical, but I find the prospect of something besides
"Systems Alliance VS _______" interesting. Just a thought.