Know nothing about fish - help me ID what I saw?

It would be helpful if you show a photo of them.

You can have just the bottom feeders in your aquarium if you wish. Although personally I prefer to have a tank full (while not overstock) of different species of fish.

As someone who has never paid attention to fish keeping, it might be more complex (but not difficult to learn) than you think to get into the fish keeping hobby.

The most important thing to begin with is fishless cycling. To learn more about the basics, I highly recommend you to read through the fish articles in our library section. We have covered most of the "must know" beginner issues.
http://petskeepersguide.com/library/fish/

If you have any more questions after read through the articles, feel free to ask.