1. Will the editor allow us to have the water surface react to explosions and units passing by ?
No, there won't be any physics effects involving water.

2. Will we have the possibility of having units evolve under water in the editor ?
Water is only decorative, it won't have any gameplay effects. Units won't be able to go "under" water. Although, you may be able to simulate this to some extent through triggers and data modification.

3. Will the Ultralisk upgrades change his visual appearance ?
Depending on time, we would like to have various upgrades be able to be seen visually on the units themselves, similar to the Marine's shields. However, it has not been determined which upgrades will be seen yet though, as the art is still WIP.

4. The plasma turret of the Battlecruisers seem to have disappeared (Q&A 40) will we find something similar on another unit ?
With the Siege Tank already doing splash ground area of effect damage, the plasma turret was not needed, as it would overlap as the same role. If you are referring to the visual of the plasma turret, not other unit currently has that ability, although it will be available in the map editor.

5. The Firebat has disappeared, what other close combat units do we have ?
Terrans currently have no melee units for multiplayer. The Firebat will however be seen in the single player campaign.

6. Do the burrowed Zerg see the units on the surface as they are or will they only see the movements like the Terran radar does ?
Burrowed Zerg units will have a very limited line of sight. If the enemy unit does walk over them though, the Zerg player will be able to see their units clearly and be able to identify them (unlike radar).

7. In the original StarCraft two Psi-Storms at the same location will not double the damage, will this stay the same in StarCraft II ?
Yes, this will stay the same in StarCraft II.

At the moment, there is 'light' and 'armored' armor classes. Buildings also fall under the 'armored' armor class.

Attacks on the other hand are a bit more varied. There is bonus damage towards, 'light, armored, biological, and massive.' Knowing a unit's damage bonuses will be very important in knowing what to use to counter certain units.

Biological units usually just mean they are not mechanical. Marines, Zerglings, and Zealots are biological. Non-biological units does not however mean they fall under the 'armored' class though and vice-versa.

For instance, Marauders are biological units but are armored. Nullifiers are mechanical units, but have light armor. Ultralisks, would fall under massive, biological, and armored. Though Battlecruisers would be massive, mechanical, and armored. These new categories also allow for many more soft counters in the game as well, giving slight bonuses to units against a certain type, but not have it as an overwhelming hard counter, where one unit wins the game easily.