You can market almost anything on facebook ppc as long as it meets fb ad guidelines. I've ran ads for diets, insurance, lead generating software, investing, etc.

In my opinion, and this doesn't apply to everyone because some people are killing it with facebook, FB isn't the best place to advertise. Granted, the CPC is a lot lower for highly competitive keywords when compared to google and bing but the majority of people who are on facebook aren't looking to buy something or are in a buying mode. You have to consider that many people on facebook aren't really looking to buy something. They mainly use facebook for social interaction.

On the flipside, I did have some success running facebook PPC. Just create good ad copy and try it out. It's relatively cheap and can provide you with a good starting point. Depending on your product, you could try just posting a quick review in your status and link it to your affiliate site and test the waters that way. Only your friends will see it but it might help you see if it will convert.

You can advertise anything on facebook. I think Facebook team has done so well dealing on this question, I mean they have tons of option on the way you can advertise and which one will fit your program.
You can advertise aff program, your portal, anything. They have so many options, including real events in your local area.
That's awesome.

I think why you're confused is because they have too many options, all you have to do now is to focus to 1 or 2 things, work on that options.
Maybe the easiest way is to try to promote affiliate program while building a list of a targeted prospects