Evan,

Time has always elapsed between base coat colors as well as base coat to clear coat. As David said, I always lightly wet sand the tape lines with 600-1000 grit. I also scuff the entire base coat with red scotch pad. I have never had a problem with paint adhesion using this procedure. I also have not had occasion to use the flex agent, so I cannot advise on that. You have your ratios figured correctly.

Let us know how it works out.

Dennis