Problem with Crouch Script - 3D C#

I cant seem to work out what the problem with my script is, here it is below:

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent (typeof(CharacterController))]
 public class FirstPersonController : MonoBehaviour {
 
     public float movementSpeed = 5.0f;
     public float mouseSensitivity = 5.0f;
     public float jumpSpeed = 20.0f;
 
     float verticalRotation = 0;
     public float upDownRange = 60.0f;
 
     float verticalVelocity = 0;
 
     CharacterController characterController;
 
     //Crouching
     private float crouchHeight;
     private float standardHeight;
     private bool crouching = false;
     private GameObject mainCamera;
 
     void Start () {
         //Cursor.lockState = CursorLockMode.Locked;
         characterController = GetComponent<CharacterController>();
         mainCamera = GameObject.FindGameObjectWithTag ("MainCamera");
         standardHeight = characterController.height;
         crouchHeight = (characterController.height / 2);
         crouching = false;
 
     }
         
     void Update () {
         float rotLeftRight = Input.GetAxis("Mouse X") * mouseSensitivity;
         transform.Rotate(0, rotLeftRight, 0);
 
 
         verticalRotation -= Input.GetAxis("Mouse Y") * mouseSensitivity;
         verticalRotation = Mathf.Clamp(verticalRotation, -upDownRange, upDownRange);
         Camera.main.transform.localRotation = Quaternion.Euler(verticalRotation, 0, 0);
 
         float forwardSpeed = Input.GetAxis("Vertical") * movementSpeed;
         float sideSpeed = Input.GetAxis("Horizontal") * movementSpeed;
 
         verticalVelocity += Physics.gravity.y * Time.deltaTime;
 
         if( characterController.isGrounded && Input.GetButton("Jump") ) {
             verticalVelocity = jumpSpeed;
         }
 
         Vector3 speed = new Vector3( sideSpeed, verticalVelocity, forwardSpeed );
 
         speed = transform.rotation * speed;
 
         characterController.Move( speed * Time.deltaTime );
 
         if (Input.GetKey (KeyCode.LeftShift)) {
             if (crouching) {
                 characterController.height = standardHeight;
                 characterController.center = new Vector3 (0, 0, 0);
                 mainCamera.transform.localPosition += Vector3(0, crouchHeight, 0);
                 crouching = false;
                 return;
             }
 
             if (!crouching) {
                 Crouch ();
             }
         }
     }
 
     void Crouch() {
         characterController.height = crouchHeight;
         characterController.center = new Vector3 (0, -0.5, 0);
         mainCamera.transform.localPosition.y -= Vector3(0, crouchHeight, 0);
         crouching = true;
     }
 }

Here are the errors that come up: Assets/FirstPersonController.cs(62,71): error CS0119: Expression denotes a type', where a variable', value' or method group' was expected

Assets/FirstPersonController.cs(75,70): error CS1502: The best overloaded method match for UnityEngine.Vector3.Vector3(float, float, float)' has some invalid arguments Assets/FirstPersonController.cs(75,70): error CS1503: Argument #2' cannot convert double' expression to type float'

Assets/FirstPersonController.cs(76,57): error CS0119: Expression denotes a type', where a variable', value' or method group' was expected

If anyone could help, I would be very grateful :D