Army lists ?

Generally you can have as many HQ's as you are prepared to buy Tony.
The issue really with any restriction is that most players tend to use OOBs (Orders of Battle) or actual organisational charts - so the number of HQ's is dictated by that.
So an arbitrary restriction of x' number of HQ's per ,000 spent would restrict most OOBs.
The rules are not generally designed for open competition play and even if they were to be used that way i would expect a tournament umpire to intervene to avoid 'gamey' lists

There is also a matter of interpretation - a Soviet tank formation might have a low value HQ per squadron (for example) as that might better represent the closeness of command. Whilst a better quality parachute force (british, German or American - even maybe Italian) might have more better quality HQs than a standard regular infantry formation.
HQs are a command network - rather than an individual group of men or vehicles.

You could of course technically get a ridiculous situation where a player could construct a table-top force with 1 HQ for every Main Battle tank he buys - it would allow huge flexibility, also create a very long game turn for the player concerned, but I am not convinced he's end up with a satisfying game (his opponent certainly wouldn't) or a win for that matter.
HQs do not add to the break-point of the army, so unless they are very cheap (so low CV HQs) there probably wont be that many even in this scenario.

I have played with a formation with a lot of HQs and it was not an advantage - I just increased the number of command blunders I seemed to throw Cheesy

but that might just have been my bad-luck!

As far as assets goes, again it is very arbitrary to try and create a restriction on artillery or air support (for example). Because, again we are playing with a simulation of what a typical force might have had, when trying to create the lists. When the reality is that in certain historical instances overwhelming artillery support might be given to a small but critical sector of a battle front, purely for tactical reasons.
But also please bear in mind that you need to buy the guns/planes to deliver the assets and these are restricted to an x' per ,000 ratio and in some instance to an actual number 1 or 2 or 3 etc. for an entire force.

I hope that makes sense?
Cheers
Mark
PS: If you trythe 1 HQ per tank unit scenario I'd love to hear how it got on Wink