Hey,
Saw a lot of good advice on army structure so I thought I'd offer some musings on modern military structure......
You specifically asked about Armored Cavalry, which, at least in the US Army, serves a different function from regular Armor, Infantry, or Mechanized Infantry formations.
Armored Cavalry fills a roll that is best described as "recconaisance with a heavy punch". They are a mix of tanks and infantry fighting vehicles (also known as APC's - think Chimera's), but they do not carry much infantry. Instead they carry a few infantry scouts.
Armored Cavalry regiments were intended to serve as screening forces for Armored and mechanized divisions, but they have a great deal of integrated support built into their structure and are quite capable as offensive units in their own right.
A comparison to other units would work as follows:
A standard platoon in the US Army is comprised of 4 vehicles, be they tanks or APC's.
A company is typically 3 platoons, plus 2 command vehicles (and associated support vehicles) for a normal total of 14 tanks in a pure armor company or 14 APC's in a pure Mech infantry company. Normally however, units are task assigned in order to blend capabilities, so a tank company would usually give up 1 platoon of tanks to a mech company, and receive 1 platoon of APC's (and their infantry) in return.
An Armored Cavalry regiment does not use the standard Company/Battalion structure. Instead they use the old horse cavalry designations of Troop and Squadron respectively. A Troop is the equivalent of a Company, but includes 4 platoons instead of 3 - 2 tank platoons and 2 APC platoons - plus the 2 command tanks for a total of 10 tanks and 8 APC's
The Squadron is analogous to a Battalion except that again, it works on the principle of 4's. A battalion would normally have 3 companies. A Squadron has 4 Troops, so at the Squadron level, you have an almost 2 to 1increase in size over a battalion.
Keep in mind, however, that the APC's in an armored Cav Unit do not carry regular infantry.
A regular platoon of 4 APC's in a mech infantry unit carries an Infantry platoon - really think of it as an infantry platoon with it's own attached transports. About 20 - 30 dismounted infantry plus vehicle crews.
An Armored Cavalry Scout platoon with 4 APC's would typically carry about 8 to 12 dissmounted cavalry scouts, whose job would be to conduct recconaisance on foot in advance of the mechanized elements, or where stealth was needed.
An Armored Cavalry Regiment contains 3 Armored Cavalry Squadrons, plus an Aviation Squadron of Attack Helicopters, and other associated support elements (artillery batteries etc...) but does not typically contain any regular mechanized infantry.
That doesn't mean you couldn't include them in your IG force, Just wanted to give you some flavor. In IG, you have to bring Infantry to bring Chimera's, and if you want an Armored Cavalry feel, you need to have a mix of Chimera's and Russ's (of whatever varient).
An all Tank force would be an Armored spearhead, not Armored Cavalry. I'd try bringing Mechanized support squads for the regular IG HQ platoon, these smaller 6 man squads - especially the special weapon squads, would feel more like Cav Scouts than infantry when tossed in the mix...
just some thoughts