What exactly do you need help with?
I need help on how I would go about doing such a thing.
Oh I see,....well putting aside the fact that I don't know exactly how you are envisioning the "thing" you want to do...from what I envisioned through your description here's what I would do.
1) Put the green screen footage over the shaft layer, key out the green screen & animate the position so it appears be falling down the shaft.
2) Pre-compose the footage of the guitarist using a mask to achieve the triangle.
3) Duplicate the pre-composed layer as many times as needed and apply the desired rotation by applying key frames.
4) Add a few lights
Every element must be a layer. It will be easier if there is no camera movement. To create a triangle with a video playing inside you can either create a triangle shaped mask on the layer and then position the layer in your composition or you can create a triangle and place it above the video, then set the triangle layer as a track matte for the video and pre-compose the pair of layers. You'll need a separate layer or a separate pre-comp for each video playing in a triangle.
To position the triangle layers as if they are forming kind of a tunnel you'll need to first create a camera and position it as close as you can to the same position your camera had when filming the actor. In other words if the camera was above your actor 6 feet and about 3 feet in front of his position then your AE camera would have to be proportionally the same distance above and in front of the comp center. As long as the position of the camera matches the camera used to film the scene it is going to be fairly easy to position your video triangles. Just turn them into 3D layers and arrange them around the keyed out actor.
You'll also have to do something to create the tunnel effect. There are lots of ways to do this.
When setting up these kinds of effects shots it is important to do some planning and then take some notes, and then get your original footage shot correctly so that you can produce the effects you ant to produce. Personally I make sketches and story boards to figure out how I'm going to do this kind of thing and then I'm very careful when shooting.
If you have no idea how to do any of the things I described then start here to learn AE: Basic Workflow
When you get a handle on that then type animating the camera or 3D layers in the Search Help field at the top right corner of AE and follow the links. I can't point you to a tutorial that will exactly reproduce your effect because I'm not exactly how you are going to shoot the shot or what your are planning except a tunnel made of videos playing back on triangular screens.