Slitherine

What kind of units will I be able to recruit as core units? Just Imperial Guard units, or also units like Space marines? Or even more exotic ones?
Will there be "hero" officers like in Panzer Corps which give the units some advantages?
Will the Space Marine units be all equal regarding their combat abilities, or will their attack and defence capabilities for example differ from Chapter to Chapter?

Look at this thread which contains links to previews which should answer most of your questions. The previews seem to indicate that the different Space Marine factions have different abilities (eg. Salamanders being resistant to heat).
viewtopic.php?f=235&t=50034

Thanks for the link, but the previews just answer some of the questions. Yes, space marines will have kind of different perks, but it doesn´t answer if their battle specifications are the same beyond that. I want to know if one chapter has perhaps advantages in hand to hand combat, close combat or ranged combat. The same question is there regarding the imperial guard units. Will they all have the same specifications, or will they have a kind of perk that gives them advantages under certain circumstances or will some regiments from certain worlds be better in hand to hand combat, ranged combat and so on.

The previews say that space marines will be playable, but not if they are support units for certain maps, or core units under the full control of the player, including changing the equipment.

I hadn´t read anything about "heroes" for my units. We will play alongside Yarrick for example, but will my units create some little heroes of their own? And no word about kind of units I will be able to have as core units. Imperial Guard I guess is a given. But who else? Some troops from the mechanicus? As airborne units belong regularly to the Imperial Navy, how about my air forces?

So still a lot of things I would like to know, to have answered if it is possible and the devs are already allowed to reveal it.

As troops gain experience, you can give them various perks. So it could be that most troops start out standard and then you get to specialise them in certain areas, making them better at hand to hand or ranged fire or whatever. I'm just guessing here though??

I did read somewhere that there will be over 300 different units in the game, so there should be quite a bit of variation.