The Alfred all in one course is a pretty good choice for a self learner. However, if you can get a teacher that would be advised. A teacher can help prevent you from developing bad habits which can hamper your progress in the future. Of course, time and expense may make that not a practical solution for you. If you're going it alone, probably the best advice I can give you is to focus on relaxation. The mark of any great athlete (and make no mistake, playing piano is an athletic activity) is the ability to use only the muscles needed for a particular movement and to relax the others. Pay attention to your whole body when you play. Are your shoulders raised and tense? Are you elbows flaying outward like chicken wings? do you feel tension in your wrists? Relaxation is a crucial habit to develop.
Now, If you haven't found it yet, there is a thread on this forum for each of the three levels of the Alfred Adult courses. It's a great place to get encouragement and to get any questions you have about the pieces answered. I'd suggest popping into the book one thread and introducing yourself
As far as other methods, I would suggest that Rachel Jimenez's "Fundamental Keys" book would be a GREAT supplement to the Alfred's all in one course. It's an adult beginner method that is built entirely around playing classical repertoire.
You can go to Fundamentalkeys.com to check it out.
Another great choice is Carl Humphries' Piano handbook (which can be found at amazon, or any book store could order it for you). In my opinion, the book moves way too fast for a beginner (especially a self learner), But once you've got some experience it is an absolutely wonderful resource.
Anyway, Hope that helps.