now I've gone and started writing stats and such... gosh darnit...
Well my theory for a Covenate army design would be as such:
2 army choice, brute or elite. The elites will have more flexible unit options, but overall not be able to field as many elites as the brutes can field brutes in their army.
Aside from an all Grunt large cannon fodder unit; the basic unit is 7 Grunts, 2 Jackals and 1 Elite/Brute. A special squad of 2 Elites/Brutes and 8 Jackals for Jackal Phalanxes. Annnd a special ops squad with upgrade such as Fuel Rod cannons and cloakers available too.
In addition lone singular units....
Golden Assassins, Jackal Snipers, Brute special: Suicide Grunt... Banshees, Ghosts, Wraiths, and Brutes get access to Spectre's and Choppers.
The Spectre would be very useful as I would let it deploy a Brute Command Squad rapidly...
Oh and Phantoms and Spirit Dropships.
Needler would be a high rate of fire weapon and even have piercing 1, but poor range (12 inches?) 2D6 Piercing 1...
Plasma Pistol would be better range (18-20?) 1D6 Piercing 1, but if Readied first would gain Piercing 3? Or some other useful trait... perhaps Piercing 2 and use a D10...
Plasma Rifles, would be the same range and just be 2D6 piercing 1, and really only be used by Elites (which I would aim for a cost of around 50 points)
I would notably just not have Covenant Drones, as they would clash with bug armies...