What I found to be helpful in transitioning from piano to organ, and fun too, is to pick up a Blues Keyboard Instruction book and start practicing songs written in the style of Slow Blues. Slow Blues typically involves solo runs (i.e., riffs and motifs)using the right hand, chords in the left hand, and a walking bass line which can be played by the bass player or by the organist using the foot pedals. As the name implies, these songs are slow which means its fairly easy to master the pedaling technique and the 12-bar blues chord progressions are also pretty standard (e.g., I-IV-V, etc.) but you can get as complex as you want. Good Luck