Hi !
Hmm I’m not really sure because I’ve never done something like that, but I think that you can change the camera position thanks to specific socket of your skeletal mesh (you can create a new one). You have simply to attach your camera to this specific socket.
Then for the zoom effect (translation of the point of view), using a Lerp would be good I think.
The inside of the scope : a simple texture with a cross inside, and the translucent part (so a square where only the dark cross have Alpha =1 (or something like that).
And for the lens, I’m sorry, but I don’t know how you can do that … 