1. Is there a limit to the number of walls and action cards you can donate to your teammate?
There is no limit.
2. Can you build walls on your teammate's village?
No. Walls can be donated to the teammate but must be built by him/her during the appropriate phase of the turn.
3. Table talk? (What's the appropriate amount of table talk between teams..if any?)
Table talk is allowed to the extent desired by the teammates/group.