I'd imagine it is common with people who's breasts were so small they broke down enough after taking T? I don't know. I've never heard of an FtM having bottom before top.
I'm considering medioplasty before top surgery because I've continually asked doctors if freeing the clitoris would give it more room to grow larger. I'm not sure how the development works, but if freeing if gave it an ability to grow larger, I'd seriously want to have medioplasty before top surgery.
I do think that approving the surgeries in that order could be problematic. But speak with your therapist, explain why you want the process done this way.