One license would do all that although we would love to sell you many licenses.
Basically Photopost Classifieds comes with 4 template types
- For Sale
- Wanted
- Help Wanted
- Personals
You can assign categories you create to different template types to achieve different sections.
Now the XML playlist thing I showed you in ReviewPost which you can easily use with Classifieds Instead works by defining an extra field in the category editor say called Feed Url. The player will load if $extra1 is not empty so as long as you do not use Extra1 on any other template types you will be fine.