I got the ranks... most of them anyways.
Minor blue
Major red
Stealth grey
Jump Pack Elites
Spec. Ops. black
Honor Gaurds (depends on if you count serving the prophet as being a higher duty than commanding fleets)
Zealots gold
Ultras white
Council Elites (ship master included I think)
Arbiter
thats about it I think
For an Elite to become Zealot... idk but it better be momentous
If you are writing book have a lot of fun with like a squad composed of stealth elites... not really ever talked about so a lot of room to play around with them. Could write it so they re the Arbiters test team composed of the best but not known by the prophets idk...
As far as tactics go think like a heavy alien ninja...
The upgrade for the scarab is only accessible during the process of it being carpet bombed;
jump to your base open the menu for the citadel and then as quick as you can press start, UP, A, A.
You can do the same thing to get a tonk.