I'd try to keep it to 15-20 pitches between breaks. So go with 5 of each or simply break before throwing your set of 4 seamers away.
Lots of my son's pens are 10 x2SFB down and in, 10x4SFB down and in BREAK;10xcurve down and in, 10xcurve down and away BREAK; 10x2SFB down and away, 10x4SFB at the top of the mask. Sometimes we split the 2SFB sets with 5 FB and 5 change ups.
Let me know what you think after you have 2 or 3 of these pens. I'd be interested in what you are seeing relative to the margin by which you are missing your targets.