Beginner to AoE, still learning. I have a few questions.

Hi r/Aoe2, been lurking around here for a while trying to study and learn the game. I saw the game on steam on sale for $3.99 and it looked really interesting and I am inspired to learn the game and enjoy it.

I've been looking at youtube videos of basic guides and the fast castle build especially because I heard its a good build you should focus on perfecting if you're new. I've been looking at Resonance22's and Zeroempires youtube channel, any others that are good for beginners?

Any other advice you have for someone who is trying to get into this game? Should I stick to playing against AI or should I just hop straight into multiplayer? Any other good build orders I should practice?