stitch in the ditch- is not a free motion technique- stitch in the ditch is a straight line (walking foot) technique- free motion is generally done with a free motion (hopping foot) with the feed dogs down (disengaged) so you can move around in curves, designs without the feet trying to feed the fabric- a walking foot with feed dogs up (engaged) makes it possible to quilt in straight lines staying in the ditch.
what ever you choose you should make a small quilt sandwich & practice so you can get a feel for the process.