1) In the gameplay video the UI is toggled on/off several times. Will that be an option in-game?

Currently, the UI will only toggle off during game cinematics. There are currently no plans to implement this for single-player or multiplayer as it would give some players an advantage over others.

2) Will the Twilight Archon have abilities?

Yes. In the BlizzCon build, the Twilight Archon had the feedback ability. We are still doing much work on this unit, so none of this is final.

3) Can Protoss Units be attacked during the Warp-In process?

Yes. When units are warping in, the unit will increase in hit points until they are at max hit points and at that point youll be able to control the unit.

4) Will there be some old units from StarCraft be included in the Map Editor for StarCraft II?

There will be units included in the Map Editor which will not be in the standard multiplayer skirmish mode. These will include various units from the original StarCraft, such as the Protoss Dragoon.

5) Will different races have different max-squad caps?

Currently all 3 races will have the same maximum population cap at 200.

6) Can the Planetary Fortress lift off?

Once the Command Center has been upgraded to be a Planetary Fortress, it can no longer lift off. Furthermore, the Planetary Fortress cannot be changed back into a normal Command Center with lift off capabilities.

Source: Battle.net