I own 7 Dark Reapers (3 very old (pre earflaps) & 4 old(earflaps), all metal), so no worries there.
I don't worry to much about the colour schemes, I just say they are a minor craftworld.
My guardians are blue with white fists and hats, with brown or black shoes. A few of them are coneheads with red hats (used as special weapon guys). They are militia, they don't need to be as uniform as the aspect warriors.
My rangers are actually not painted more than black spraypaint.
Edit: I own 7 Fire Dragons, Exarch only has access to a firepike, but no one has ever bothered me about it if it is used as a normal fusion gun.
The Dark Reapers don't have an actual Exarch, but a bigger gun (and earflaps) usually marks one model out from the rest.
Here is the what it would look like as 2 battalions:
Eldrad, Smite, Mind War, Doom, Executioner 135
Autarch skyrunner, banshee mask, laser lance, shimmerplume [Warlord] 110
5 Dire Avengers, dual ASC 58
10 Guardians, scatform 92
8 Stormies, two flamers 60
5 Dragons, Pike 123
5 Hawks, Talon 68
3 Scatbikes 69
3 Reapers, AML 100
2 Scat Serpents 268
5 Rangers 60
5 Rangers 60
5 Avengers, dual ASC 58
5 Scorps, claw 64
5 Scorps, biting blade 59
5 Spiders, dual spinners and PWblades 90
2 Walkers, dual lances 160 (separate units)
This would require me to drop something, maybe the scat bikes?
That would allow me to move the Dragons and a serpent to Alaitoc and give it spirit stones. I could perhaps drop the Spiders instead and cram in a 6th Dragon. Suggestions?