3D camera smooth rotation and mouse wheel zoom

Hi All! I have a problem with a project: a cube in which a camera moves around in the three axis with the mouse. The XY axes are controlled by mouse X and mouse Y, and the zoom (not FOV) with the Mouse ScrollWheel. There is the script that moves the camera:

 using UnityEngine;
 using System.Collections;
 
 public class CameraMotion2 : MonoBehaviour {
 
     public float zoomSpeed = 4.0f;
     public float rotationSpeed = 0.5f;
 
     float lastMousePos;
 
     void Update () {
 
         // Wheel Zoom
         transform.Translate (Vector3.forward * Input.GetAxis ("Mouse ScrollWheel") * zoomSpeed);
 
         // Camera X Rotation
         Vector2 xMouseEdge = MouseScreenEdge ((int)(Screen.width * 0.3f));
 
         if(!(Mathf.Approximately (xMouseEdge.x, 0.0f))) {
 
             //Move your camera depending on the sign of mouse.Edge.x
             if (xMouseEdge.x > 0) {
                 //Move Left
                 transform.Rotate (new Vector3 (0, xMouseEdge.x, 0) * Time.deltaTime * rotationSpeed);
             }
             else if (xMouseEdge.x < 0) {
                 //Move right
                 transform.Rotate (new Vector3 (0, xMouseEdge.x, 0) * Time.deltaTime * rotationSpeed);
             }
         }
 
         // Camera Y Rotation
         Vector2 yMouseEdge = MouseScreenEdge ((int)(Screen.height * 0.3f));
 
         if (!(Mathf.Approximately (yMouseEdge.y, 0.0f))) {
 
             if (yMouseEdge.y > 0 && transform.rotation.x > -0.5f) {
 
                 transform.Rotate (new Vector3 (-yMouseEdge.y, 0, 0) * Time.deltaTime * rotationSpeed);
             }
             else if (yMouseEdge.y < 0 && transform.rotation.x < 0.5f) {
 
                 transform.Rotate (new Vector3 (-yMouseEdge.y, 0, 0) * Time.deltaTime * rotationSpeed);
             }
         }
     }
 
     void OnCollisionEnter () {
 
         StartCoroutine (ResetPos (0.5f));
     }
 
     Vector2 MouseScreenEdge (int margin) {
 
         //Margin is calculated in px from the edge of the screen
         Vector2 half = new Vector2 (Screen.width * 0.5f, Screen.height * 0.5f);
 
         //If mouse is dead center, (x,y) would be (0,0)
         float x = Input.mousePosition.x - half.x;
         float y = Input.mousePosition.y - half.y;
 
         //If x is not within the edge margin, then x is 0;
         //In another word, not close to the edge
         if(Mathf.Abs (x) > half.x - margin) {
             x += (half.x - margin) * ((x < 0) ? 1 : -1);
         }
         else {
             x = 0.0f;
         }
         if(Mathf.Abs(y) > half.y - margin) {
             y += (half.y - margin) * ((y < 0) ? 1 : -1);
         }
         else {
             y = 0.0f;
         }
         return new Vector2(x, y);
     }
 
     IEnumerator ResetPos (float time) {
 
         float elapsedTime = 0.0f;
         Vector3 targetPos = new Vector3 (transform.position.x, transform.position.y, transform.position.z - 1.0f);
 
         while (elapsedTime < time) {
 
             elapsedTime += Time.deltaTime;
 
             transform.position = Vector3.Lerp (transform.position, targetPos, (elapsedTime / time));
         }
 
         yield return null;
     }
 
     IEnumerator ResetRot (float time) {
 
         float elapsedTime = 0.0f;
         Quaternion targetRotation = Quaternion.Euler (new Vector3 (0, transform.rotation.y, transform.rotation.z));
 
         while (elapsedTime < time) {
 
             elapsedTime += Time.deltaTime;
 
             transform.rotation = Quaternion.Lerp (transform.rotation, targetRotation, (elapsedTime / time));
         }
 
         yield return null;
     }
 }

But that have some problems... First of all at line 14: the wheel translation is no smooth (i need a sort of ease out) Second: The X rotation is activated by the mouse position Y the more it reaches the top or bottom borders of the screen, but I need that the X rotation returns back when the mouse Y returns near the center of the screen. Third: the two coroutines don't work (the animation is istance and not in the whole time setted). I know it's not a simple script, but i really need help.

PS The MouseScreenEdge is a function that calculates the amount of space from the borders of the screen.