A: Yes, this may be used in the application that you stated. Be sure to take in consideration the size and weight of the table, to be sure these boards will be appropriate for this.
A: Hector, this is perfect for both indoor and outdoor projects. For exterior use it is recommended to seal lumber using the water test to see if its time to seal. Drizzle some water onto the wood. if the water beads, the wood is still sealed and protected. if the water is absorbed into the wood within a few seconds, its time to apply a sealer.
A: Yes, you could.
A: Art, It appears that this size of common board might be a special order. Please contact your nearest Home Depot store for details.