I'll have to look up the other two foods but I vaugely recall the Kirkland being fine for a growing giant breed pup.
There is no set amount thats correct (regardlessof what the bag says). You feed the amount that keeps him in the correct body condition. Use the bag label as a starting point, and adjust based on him. Lower it if he chunks up, increase it if he gets too slim. The ideal is nice and slim.
Socialize socialize socialize. And when you think you're done, repeat it. Only got 5 minutes to spare? Take him for a quick walk to say hi to the neighbors.
By "alpha training" you mean that whole mess that includes alpha rolling as a training technique? Yah, no. Please don't alpha roll your pup. For one thing, although you might be able to make him now, he's going to quickly reach a size where you can't. If thats how you plan to controll him you'll be screwed.