Unreal Engine switched to an ‘include what you use’ style some time ago. Probably after that tutorial was made. Previously, you automatically included a lot of core stuff from a header I believe was called “Core.h”. Now you automatically include very little from “CoreMinimal.h”.
It’s likely that you are missing some includes as a result.
I imagine that your third problem is a result of this as well. I highly recommend using ‘Rider for Unreal’ as your IDE instead of Visual Studio. It’s a lot better and will help you with includes as well.
Another issue you might face following an older tutorial is deprecated functions.
That said if you know your way around documentation and so on you should be able to complete the tutorial. I would however recommend you find a newer one.
And yes this forum is the right place to ask.
Edit: As a sidenote, the include you posted for UCameraComponent can be simplified. You should be able to find the include for any base class in the documentation.
Example: UCameraComponent | Unreal Engine Documentation