It's about feel. If you know how a song is supposed to sound you can play the correct strum patterns to make it sound they way it should.
When playing in a group with multiple guitars, you have more freedom. Watch a vid of Bobby, he's all over the place most times, BUT, it sounds all right because he is with the Band.
I saw solo Bobby with Wasserman and he played totally different. He had to play in a way that allowed you to hear the song correctly.
You will eventually learn that the up stroke and down stroke may not always be back to back. Regea songs have definitive strokes in one direction.
the one the thing to note is that a down stroke and up stroke will make the cord sound totally different which allows you to utilize the direction of the stroke to shape the sound.
Try playing along with an early 70's Me And My Uncle. This is a somewhat basic, good begining song to learn. Or try After Midnight, which has a great chord progression but it is easy to play with.
I hope this helps
..I've been there before.
YOU KNOW IT'S GONNA GET STRANGER