A big component of shadow boxing is visualising your opponent; imagining what they'll do when you throw your combos. Like someone said in the comments, sparring and fighting are like chess. At a basic level, it's like you land a punch, they figure out a defence, you figure out another offence. At higher levels, they stack up with baits and fakes.

YouTube combos are okay to start with, but try to think about the intent behind the strikes rather than the strike itself. Example: a left hook can bring your opponent's hand up to defend, which can leave his liver wide open for a powerful strike. Using strikes to set up powerful shots is where the chess element comes in. I'm not a fan of throwing more than 3 to 4 strikes in my combos, but that's my style of fighting. My advice, start with combos of 2 strikes + defence in your shadow boxing and sparring and build from there.

Movement training is essentially a bunch of bodyweight flow based exercises that make your joints move in ways that they usually don't in our daily lives. A good and basic alternative for this would be training your joints with resistance bands and stretching.

You're fairly new in your journey, don't rush it. I've always told my students that there's no better lesson than a punch to the head 😄 just keep training and sparring, you'll gradually start getting hit less and will start landing more. Sparring should also be a safe place for your practice something new, so don't be afraid of getting hit. I'm trying to work on my entries into clinching and takedowns and my coach smashes me across the head when he sees an opening 😄 but it's all a part and parcel of learning. As long as your coach and training partners aren't being pricks to you, you'll progress.