Is my certified Service Dog allowed in the airport and can he ride on all of the airlines?

Yes

I believe that your Service Dog is allowed in the airport. Also, I think that you would have no problem to be on board with him, but please make sure about it with your airline before you fly.

Yes for sure

Yes. But most Airlines limit how many pets can be on the flight. Just make sure you ask and let them know you're bringing your service animal

Yes to both questions