I'm not a ref, but I will give this my best shot. Pretty sure a bonafide ref will hop in if I goon it up too much :)
1. As per the rules for M01, the innovation piece must be made of AT LEAST two white pieces. It doesn't say anything about other colors or types of pieces, so it doesn't matter. Go for it. Don't forget there is also a size requirement.
2. When the 2:30 is up, if the robot is moving, the refs will stop the robot. Only points that have actually been scored prior to expiration of time will count.
3. From the robot game rules, page 20: Here is what happens to any equipment or mission models that were in contact with the robot when it was interrupted outside home (even partly):
• If the object was with the robot when it launched: Keep it. Bring it with the robot.
• If the object was obtained after the robot was launched: Give it to the referee for the remainder of the match
If the team accidentally drops something on the table, in general that is not a problem and the refs will give them back to the team, assuming they were meant to go back to the team, based on the rules above.