Is the Art of the War Fast Castle build order in AoE 2 DE wrong ?

I've been trying my hands at the AotW missions and (after who knows how many tries) I finally scored the gold on this one.

Then, out of curiosity, I checked out TheViper's video to see how he faired at it. Throughout the mission he kept saying that's not how he'd do it and this so wrong.

After feeling slightly encouraged and thinking I've got my very first build order down, and then immediately getting discouraged to try it out, here are my questions:

1. How "wrong" is the build order in it?
2. Where can I learn the "correct" one?
3. How many do I need to learn before I give multiplayer a shot?