Level inside level

Hello, i’m attempting to create a motion graphic that gets getting complexer by the day. Right now i need to create a level in which i have a music festival stage and a bunch of crowd cheering [we’ll call this Level A] (which i may end up doing through some green screen media files). I have created multiple levels, in which i have a camera and other assets animated through the sequencer [We’ll call this levels 1-10]. So far so good.
Now then, the problem is that this video is a presentation of how a 7d concert would end up looking, so i need to somehow get the view from the camera i animated in level 1-3 into the stage of level A, and limit the view only to what the camera sees, or somehow make so that the level is constrained within a certain space (the music festival stage) while all of it’s assets are being animated.
This is what the client wants to have. But since i’m making the video as a proof of concept…

If using the camera view as some sort of crop view is impossible, then some way of adding the whole level, and limiting it with some sort of fade would also work, that way i could get the full scope of depth and move the main camera anywhere