Would love to John.
halo.wikia.com/wiki/Sangheili
That link will help for the Sangheili, who can be the most confusing to deal with as they are the primary militant species in the Covenant and prior to the Unggoy Rebellion, were the only armed species. (If you can believe it, at one point Grunts were not even armed. 
but after the rebellion, they proved themselves competent enough to be integrated into the military.)
Brutes, it's more "Who's got the fanciest head piece."
but they do follow the Sangheili example for the most part. Link here should help: halo.wikia.com/wiki/Jiralhanae
Grunts are easy. Orange combat harness indicates lowest rank(Minors), Red (Majors) for them is something like a Private First Class (so game wise I'd treat them the same)Green indicates a weapons specialist, the grunts who carry around the anti-tank weapons like Fuel Rod Guns. White armour, sometimes with a white tabard over the chest, indicates Deacons, who perform exactly as their title implies. They give religious guidance to other grunts, and so can be used as combat leaders, but they're still just a religious representative, not a tactician and even then, only members of their flock are likely to take orders from them. Not all Unggoy are true believers, not because they're cynical on the subject or anything…. many just have IQs lower than a brain damaged squirrel and can barely grasp the concept of "This end toward enemy." when handling their own weapons.
Jackals themselves don't seem to show rank through armor colour, probably unnecessary as they mostly act as scouts and harassment units. Supposedly, this is done through their shield color though, but in gaming terms, it will be pretty meaningless.
Hunters are the easiest. They have no rank, they are just a bonded pair. One worm colony split between two armoured bodies which they control by structuring themselves into something of a musculature. But, the trick there is….there should always be at least two. There don't seem to be any colonies too small to fit across two sets of armour, but there are some big enough to fit across 3 or even 4 sets.
Yan'me/bugs are simple enough as well. Green for their lower rank, red for the next one up. That was done for the video games though, in a table top game I'd treat them all the same. (Or if you use Khurasan's Vespulids to represent them, the larger guys in each pack can be the "Majors" while the others are the "Minors")
Slick blue-black armour is universally a sign of veteran and special operations units in which ONLY sangheili and Unggoy may be inducted into. Brutes are considered too stupid to be special operations and jackals are considered too untrustworthy. Occasionally, they will have Hunters with them if needed. Yan'me/Bugs are also barred from it as they are not even intentionally a combat race. Their primary duty was ship maintenance for Brutes as they were deemed too stupid to be allowed full access to their own ship's weapons, let alone given Huragok/Engineers to maintain their vessels.
Now, as for their structure…
They refer to their fireteam level units as "Files"
On average, a File will consist of four Unggoy Minors, one Major and be led by either a Sangheili Minor or a Major.
The second organizational possibility for this is substituting the five unggoy for four Kigyar.
A third version is subbing out the Sangheili for Brutes.
The next organization up is the "Lance." which consists of 2-3 (In some cases, I've heard up to four) Files. Not all files need be the same organization, except that it will be led by either Sangheili or Brute, but the two will not mingle or co-exist in a battlefield situation, nor even will be serving in the same fleet, let alone the same combat unit. The Covenant keeps a bit of Segregation where it needs to.
So, this means that a "squad" for them will consist of around 12-24 fighters, of which only 2-4 will be actual soldiers. The rest will be conscripts and only one will positively have combat experience.
There isn't a lot of detail past that but the next unit up seems to be a Cohort, probably consisting of 2-3 Lances, then a Legion consisting of several Cohorts.
Best I can tell too, Sangheili in charge of a cohort have quite a bit of knock around power and can request most anything they need from tanks to air support and specialist units like Hunters/Mgalekolo. I'm not entirely sure about how an HQ section of any sort is organized. Mostly seems to be a lone Zealot(Gold Armour) or Ultra(White). Once you get above the red armoured Majors, their colors mean less and less and it becomes more about who's who, which individual commands the most respect. Brutes do that as well, but have a pack mentality instead of an honor code to follow.
For wargaming purposes, I don't imagine giving a commander a pair of bodyguards, probably Majors, would be a stretch since Sangheili society has a heavy reliance on friendships and clans and Brutes have a heavy reliance on family.
Looking back, that was quite a long winded explanation with links, but hopefully it's a help to John and anyone else who may be interested in figuring that out.
Oh, and so far as armour and their anti-grav bikes go…. Those seem to be issued out piecemeal to the units as needed but are attached to squadrons. Possibly a means of keeping tactical flexibility while maintaining logistical ease as the Covenant rely on dropships as a means of very mobile warfare like the U.S. did in the 1960s, but they do appear to have dedicated Cavalry, Mechanized and Ground Attack Aircraft squadrons, but these may not all have dedicated personnel attached to them. The notable exception being aircraft and warships, which have dedicated pilots attached to them.
I really appreciate it. I have had the figs for a few years now but really don't play the video games so know little about the troop types. Now that can change!