Take a look at GOG's live gameplay vid with Tomek Gopp: http://www.youtube.com/watch?v=Va6bJsZ_Mjg. It should show you the two different choices for how you can control combat. Skip ahead to about 10:00 to get straight to the gameplay demo.

You don't have to spam clicks for combat to work; I believe that Tomek was proving a point that timing was not important any more.

Yeah, a mix of that and of combining hexing signs and items. There are actual combos (like fighting combos) which are environmental depending on what's around you. For example, Tomek showed a finisher off at the CDP Days where Geralt attacks and kills two enemies who are both pretty beat up; I don't know what the precise trigger was, but it seemed to be enemy positioning, their health states, and probably a combo of light and heavy hits.

There's also a more tactical element in combat now, where you prep the terrain with hexes and traps, use it to your advantage, and then maneuver to take advantage of the opportunity that you've created. This kind of tactical combat prep only seems necessary on the hardest difficulty; on the lower levels of difficulty Geralt can just wade in and chop everything up like he's making tacos or something.

Got no clue about that. Maybe try asking over on the official Witcher 2 fora.