Hello ! I happen to be a keyboardist who is trying to learn bass - pretty much the opposite direction of the one you are going in, lol ! You may want to try the 30 Day Keyboard Workout. It is in the same format as the same books for guitar and bass, and basically gives a variety of exercises that gradually get more difficult in two cycles of 30 days. I find it helpful to use to stay sharp, as I have not been able to continue with lessons.
Having said that, lessons would save a great deal of time/pain/effort, at least for 3 to six months. My experience was very similar to tplyons : once you learn enough to not hurt yourself, practising will be that much better.
Additionally, if you want to round out your theory knowledge, there's a couple of books by Dave Stewart (of Stewart and Gaskin) that I found very helpful. Understanding The Dots, in particular, is my favourite.
Finally, remember that, unlike the bass, the keyboard has several conventions that are centuries old. You may find it helpful to quickly scan some of those beginner books to get the fingerings. In fact, if I have the time, I can dig up a site that has that information.
Oh ! Dunno if you have the Bass Grimoire, or the Guitar Grimoire, but they do have a Keyboard Grimoire as well...
As I type this I found this site -
http://www.pianofundamentals.com/book/en/1.III.5.4
It seems a bit dry, but toward the middle it shows the correct fingerings for the scales. If I find more stuff like this, I will post again and let you know.