Linux permissions in the context of web sites

Hi:
I have read and reread a number of articles on permissions and know how to change them, yet I find that I cannot place them in the context of web site development and usage. I do not have access to the server directly since I use a remote Linux shared server.

As the only developer, I am creating a web site with PHP. I need to create directories and files which I transfer through an FTP app on my desktop. All of the web site scripts and data files are in the URL-accessible server directories, except the uploads directory that is private (between the URL-accessible web directory and the root directory).

Directory structure:
/
-private directory (Non-URL accessible - for uploads)/
    -files
    -sub-directory/
        -files
-web directory (URL accessible)/
    -sub-directory/
        -files
        -sub-sub-directory/
            -files

There are three types of user:
1. The only developer, where I create directories and files, use the web site app, upload image files from the web site and the FTP app, and manage the directories and files through FTP.
2. The web site user, who uses the web site forms and reads data on the web pages. They may not upload any files. They have no personal access to the directories and files.
3. Specific web site users, that is registered members, are like user 2. except they may upload image files to the server.

What is an permission 'owner'? Me as developer, the server, or the scripts?
What is a 'group'? Me as a developer, only other developers if there were some, registered members?
And is 'other' the regular non-registered users - ie anybody using the app?

For each of these groups 1 through 3, what would be the rwx permissions for the directories and files that they have access to?
If another developer joins me and I want to have secure directories and files that this second developer must not have, how would this change the permissions?

Much appreciated :)