Blocking updates for document library

Scenario:
For one of the new requirement we needed to block all updates to documents in document library

1. User should able to upload a new document
2. User should not be able to upload a document with the same file name as existing document
3. User should not be able to edit metadata once it has been entered.

Solution:
Simple event receiver did the trick but as always with some learning / gotta's.

Assuming 2 different situations
1. Simple document library with no extra metadata columns : In this we will need ItemAdded event to update the event once.

2. Document library with extra properties : We dont need ItemAdded event and code can be commented.

Code:

using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.SharePoint;

namespace SKN
{
    class EventHandler1 : SPItemEventReceiver
    {   
        public override void ItemAdded (SPItemEventProperties properties)
        {
            base.ItemAdded(properties);

            //DisableEventFiring();
            //properties.ListItem.Update();
            //EnableEventFiring();
        }    

        public override void ItemUpdating (SPItemEventProperties properties)
        {
            base.ItemUpdating(properties);

            if (!string.Equals(properties.ListItem["Created"], properties.ListItem["Modified"]))
            {
                properties.Cancel = true;
                properties.ErrorMessage = "no update";
            }
        }
    }
}