Ship rotation while moving forward

I am making ship move to mouse click. The ship goes to where i clicked, and the ship even rotates before it moves towards the click. The only problem i see is that when the ship moves forward, moves from speed 0 to the speed i set it too. I have tried using Lerp to accelerate smoothly before moving and slow down before stopping. The ship however takes the same amount of time to get from point A to point B regardless of distance, so things look funny.

If someone could help me out with this, that would be awesome. I need to find a way to add acceleration to the ship. And for a plus, it would be amazing if you guys could tell me how to make the ship move forward so the ship makes a small semi circle before heading towards the direction i clicked.

Here is the code i have so far.

 public float speed;
 private Vector3 endPoint;
 private Quaternion rotation;
 float tempTime;
 bool start_time = false;
 float half_way;

 void Update() {
     float step = speed * Time.deltaTime;
     // if left mouse clicked
     if (Input.GetMouseButton (0)) {
         endPoint = Input.mousePosition;
         endPoint.z = 20.0f; // position of main camera on the z axis
         //get endpoint relative to the camera
         endPoint = Camera.main.ScreenToWorldPoint(endPoint);
         // set rotation value
         rotation = Quaternion.LookRotation (endPoint - transform.position);
         tempTime = 0.0f;
         start_time = true;
         half_way = (endPoint - transform.position).magnitude / 2;
     }

     transform.rotation = Quaternion.Slerp(transform.rotation, rotation, (Time.deltaTime * speed / 4));
     if (start_time) {
         tempTime += Time.deltaTime / 8;
     }
     // if rotation is half way done.
     if (tempTime > step){
         //get direction
         Vector3 dir = endPoint - transform.position;
         // distance from A to B
         float distance = dir.magnitude;
         if (distance > step) {
             transform.position += dir.normalized * step;
         } else {
             transform.position = endPoint;
             transform.rotation = rotation;
             start_time = false;
         }
     }
 }

Thank you in advance.