Does defensive mode do anything else besides give you 2 counter attacks? Do missile units get 2 counter attacks also?

How far away do you need to be from an enemy to take-over a building? Is it the distance of the enemy from the building or from your troops?

How many turns before a player goes inactive?

How do the heavy cavalry and marksmen bonuses work?

Q: Does defensive mode do anything else besides give you 2 counter attacks? Do missile units get 2 counter attacks also?

A: the primary reason for defense mode is the +10 defense bonus (at the cost of -5 attack, but overall, the stats gain 5... so I think it's a good trade)

I can't answer the multiple counters thing because it's always been kinda glitchy in my experience... I see units in defense often not get that 2nd counter then sometimes they will...

Q: How far away do you need to be from an enemy to take-over a building? Is it the distance of the enemy from the building or from your troops?

A: When I was last playing regularly, the answer was 6 hexes... but I've seen recently that I was 5 away and still had my goldmine taken over... so it's hard to say now. I do believe that the hex count is from the one you click... but it could have changed to be from where your troops stand now for all I know.

Q: How many turns before a player goes inactive?

A: in what? a camp? I'd guess 3-5...

Q: How do the heavy cavalry and marksmen bonuses work?

A: This takes a more complex explanation of the way that troops work in general, so here goes...

when you attack with a normal melee troop, the damage you deal is somewhat random within a range. You might notice under damage for a unit, it'll say something like "5-7"... that means that at base stats on both ends to a neutral troop, it should deal anywhere from 5 to 7 damage per troop in that stack.

the heavy cav bonus would essentially make it ALWAYS do the 7, because it's set to the max damage (of course, cavs do way more than 7 damage... but that's just an example).

for ranged units, the their damage gets reduced the further away the arrow has to fly. You're more likely to strike critically right up in someone's face than yards away, right?

maximum damage output for ranged units is at 2 hexes away (1 hex blank between you and the target) and for every hex more you move away, you get a reduction in the potential damage.

marksmen are such a good aim though that they suffer no such pentalty... they can happily do regular damage at even 9 hexes (tower) away.

Li, as usual a fountain of great knowledge

I found in the manual some more info on the heavy cavalry charge.
Special Abilities :
Charging Assault : For each space moved before an attack add +2 Attack.

It also says.
Commandeers Special Abilities :
Attack Aura : +2 Attack to neaby (<Reqs typo) armies per troop. Each troop gains best Attack Aura only.
Commandeers are able to take command of any enemy building as well as boost nearby troops moral increasing their damage up to +50%.
How far does the aura extend? Is it better if your closer?

I believe it is three hex

yes, 3 hexes. 1-3 is exactly the same bonus, no need to be closer.

Thanks a lot for the help.