Hi!
Hello!
Is the base type of an HQ unit class plays any role?
Yes and no. No, because the base class of any ground unit does not change how the attached component functions. An HQ1000 on an infantry base functions exactly the same as an HQ1000 on an ultra-heavy vehicle base. Yes, because the choice of base class determines the cost and survivability of the HQ unit.
Going out of order for a second to address an important preliminary point:
I understand that light vehicle has more Hit Points, but I always mark "Avoid Combat" for HQs, so I do not think that Hit Point are very important for HQ units. Am I right?
It still matters, because your HQ units can still get hit ("Avoid Combat" only reduces those odds, by 75% or 80% I cannot remember which) and if they do get hit, you want them to survive if possible.
What is the difference in Infantry HQ with capacity of 1000 and for example a light vehicle HQ with the same capacity of 1000?
Why do I want to make light vehicle HQ (transport size 22) instead of infantry HQ (transport size 10)?
There are two things which are important here:
(1) the differences in armor and HP matter for HQ survivability, so the LVH version for example you 'pay' an extra 12 tons to get about 16x better survivability against light weapons fire (CAP, PW, etc.) - of course, if you get hit by a heavy anti-vehicle weapon it makes very little difference, but light weapons are usually the most common by far.
(2) The tonnage/size matters very little. Even for the example you're giving here, 12 tons out of 1,000 is only a 1% difference, a very small price to pay for a big survivability improvement. In reality, the price should be much less, because 1,000 tons is a very small formation size, in fact it is impractically small unless you are extremely committed to roleplaying a detailed OOB. Base formation sizes should probably be in the range of 15,000 to 20,000 tons in which case +/- 12 tons is imperceptible.
The other key thing to think about with HQ units is the cost. The HQ component costs significantly more per ton than any other component type except STOs, and has a maximum component size of 250 tons beyond which the cost keeps increasing while the size stays constant. This means that large, high-capacity HQs will be very expensive. Now, if you have an expensive HQ and then you add armor to it, armor multiplies the cost of a ground unit so the expense becomes that many times greater. So for a small HQ, say a brigade command of 20,000 tons (component cost = 8 BP), even though the cost per ton is large it will be a relatively minor part of the total formation cost, so you can feel free to armor it up for maximum protection and it will not cost you too much more. However, if you have an army-level HQ commanding 500,000 tons (component cost 200 BP)... this is already extremely costly, and placing armor on it will multiply this and make it the dominant part of your formation build cost.
For this reason, for high-capacity HQs I usually prefer to use the Static base type with minimal armor. This is a good deal because for an extra 12 tons (a very small premium if your HQ component size is already the maximum 250 tons) you get triple the HP and thus 9x the survivability against light weapons. Sometimes I will deviate from this for roleplay reasons but in general it is a good way to go once you hit that HQ component size cap of 250 tons. For the smaller HQs that command your lowest-level formations, these are fine to armor if you want since those formations are usually in the front lines anyways.
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By the way, in general with ground units both cost and size are important for different reasons. The less your formations cost, the more of them you can build, which is great since ground force construction capacity is usually the limiting factor (you need multiple millions of tons of ground forces to invade an NPR home world...you will need to build a lot of units!). The only importance of size comes when transport capacity is the bottleneck, which mainly means on the offensive when invading a heavily defended planet. In this case, 20,000 tons of ultra-heavy vehicles may be very expensive to build, but this gives you the most combat power per ton when dropping your first invasion wave and that in turn gives you enough time to get the following waves into action. By contrast, usually when defending you are not limited by transport capacity since your defenders are already in place, therefore you want to have excellent cost efficiency to build as many defenders as possible before the invaders come.
This also interacts with the cost of building your troop transport fleet. Of course, you can always build more transports to increase your maximum tonnage, however building troop transports is expensive in its own right, especially if you build heavily-armored dropships for invasions, so in many cases it makes more sense to pay those costs to build heavy armored units that are more efficient per-ton, especially since ground units cost Vendarite which is usually plentiful while troop transports cost Duranium, Neutronium, Gallicite, and other potentially more valuable minerals not to mention a valuable shipyard that could be used to build something else.
