No.
Yes. Think Bots from Unreal Tournament.
Yes, only single player. You will get hundreds of nondescript MP invites during your single player experience, but they are no big deal at all.
Really, you should download the demo from Steam and try it out. Its awesome, if youre into tactics.
Tip: Play the opposing side's (red guys) moves. Try to account for every possible movement of the enemy and position your soldiers accordingly, even if its strictly a defensive position. Learn to use "Continue on Sight" and "Engage on Sight" effectively. Remember, if you want your soldier to move quickly from one position to another, you must "Cancel Aim" as a first step.