Prevent Concurrent Editing of a List Item

you do not need any workflow or event handlers ( still you can use them for your purpos but they will slow down the performance if you will be having a lot of items)

go to setting --> list settings click on Advanced Settings

in Item-level Permissions in read access select all items and in the same place in Edit access select only their own

and in permissions give list members a contributer role

for the suppervisor you can give him higher permission i think designer will work, or simply you can give him full controle on the list

A few ways to approach this:

Start with a picture library

Add additional columns to the base set for storing the profile information you need. This is very simple and the list can be very simply managed using out-of-the-box views. Users are added by uploading their image and filling in their personal details.

Start with a contact list

Add a picture column for the user's image. This would require the extra step of the user having to upload their image somewhere. I would discount this option over the previous one as there are no significant advantages and you have to deal with the extra step.

Use My Sites

This gives each user their own private and public page and has the advantage of being initially populated from Active Directory. Users can upload a picture of themselves and you get other nice features as well.

However this won't give you the list you're looking for - you would need write a web part to query the profile data and display it as a list. Features to only display certain users and/or for editing a user's profile information may also be needed.

This can be a nice powerful solution but could also get complex quickly and may be overkill for what you need. My Sites should be planned carefully and require user education.