You can give more than one user the same home folder. So when they login they will see files uploaded by other users in the group.

To make this folder read only uncheck the group write permission (or change the Octal value to 755). The folder remains writable by admin but becomes read-only to other users.

The procedure to make files read only is similar, the Octal value for a read-only file is 644.

And don't forget you need to do the same for any further files you add or sub-folders you make.

As we don't control your domain you have to do this yourself. The principle is that you need to create (or get created) an "A" record in your domain pointing ftp.mydomain.com to the fixed IP address of your FTP site.

Login to your control panel, you'll see your IP address displayed. The mechanics of setting up the "A" record vary. You may have to ask your ISP/connectivity provider to do it for you, or they may have a control panel where you can do it yourself. If you work for a large corporation check with your IT department.

Once the "A" record is setup you should be able to immediately connect to your site at the address you have chosen.