Keep in mind that we're a very small community theatre, so getting really experienced directors are sometimes hard.  So this summer it's me.

I'm directing my first full sized musical - Bye Bye Birdie - and I could use some input.

Last night was our first rehearsal and things went very well, but I could use some insight.

I tried to do most of the blocking ahead of time at home, but when I got actors on stage and started watching them I found myself moving them around in a different manner than what my notes showed.

I'm wondering if I need to change my approach ... as in ... I pick certain spots within the dialogue that I know they need to be at a particular place, but everything in between ... leave it loose, see how they "feel" what they need to be doing move as necessary.  All the time my SM takes notes as well. 

Does that make any sense?  I would appreciate your thoughts.

What you do sounds fine if it's working for you.  Have exact notes is VITAL.   Don't keep changing major blocking points.   It drives some actors crazy.

I think you are smart to leave a little flexibility for new inspiration during rehearsal. It is good that you planned ahead, but sometimes things look different on paper. Trust your instincts.