Shana,
If you want to get into and enjoy recording, don't jump in headfirst. It would be crazy to strive for perfection when you first start out, simply because "true perfection just doesn’t exist", you also don't have the skills that can only be acquired with time or a multi million dollar budget.
Other equipment you can buy really just adds to your songs. The difference it can make is significant, but not a necessity, especially for home recordists.
A good place to start would be to just learn your equipment. I think one of the best ways to do this is, just record everything you do. When you are just mucking around record it; that’s normally when I find ideas that could be developed. The BR-8 takes 100 MB Zip disks i belive, and on standard mode is capable of recording 50 mins, so keep a few spare so you can come back and listen to your tracks a week later. As you are just experimenting with vocals or guitar, play with your microphone position. You can learn allot, when you are just listening back over what you have recorded. You will learn what sounds you like best and how to achieve them.
Also run parts of what you record through the BR-8's built-in FX, it will help you understand how all the FX work and what they do.
If you master your own equipment you will then be able to decide where you want to take your recording (and what it's lacking), and what extra equiptment you will need if any.
MP3's are an audio format. It is primarily used for songs over the Internet. To convert your saved music into MP3's you would probably need to run one of the outputs of you BR-8 into your computers sound card, and convert the signal using one of the various MP3 software packages.
Above all remember to have FUN!!! (don't let all the technical talk turn you off)

omnipotent