This part might be unnecessary, depending on your web server configuration. It's all about making sure that your web server can access the files from your website. The following screenshot shows a simplified graphic without MySQL involved to illustrate the communication between the web server and the files:

The web server can run under a different user than the PHP and the files can be owned by a different user again. To make things even more difficult, you can use groups instead of users as well. It's pretty hard to predict the configuration of your server; there is therefore no single solution.

If you're running suEXEC or suPHP on Apache, then all the elements run with the same user making your web server more secure, and easier to use in this case. The web server can access and write the files by default; there's no need to change anything.

Accessing (reading) the files shouldn't be a problem. Files written by the FTP server are almost always readable...