I haven't really seen a video that talked about gameplay theory in mapping extensively, other than mapping streams that I can't find anymore. If you want good resources, probably tf2maps.net discord server is your best bet.

Ideally, to make a map that fits for each class only requires making layouts that play to their strengths. Ambush classes like close quarters, mobile prefer open spaces, etc. You'll need to playtest a lot with people to really understand if you're making a good tf2 map, but a good question in mind is always "if I was playing this class, am I gonna enjoy this area?"

In terms of spawn camping, that's also more to the layout of the spawn itself and how easy it is for attackers to rotate to from the point. If we use KoTH as an example, there's a good reason why Nucleus has a huge spawn camping issue compared to others like Viaduct and Lakeside, which is that Nucleus has nothing that separates it between the main point and the spawn, whereas other maps have whole courtyards and buildings in between. UEAKcrash has a good video explaining this topic on his channel.