I'm not too sure if 4 weeks would be worth it. At 12.5mg your unlikely to feel any side effects as these only seem to kick-in at 25mg. Why not do something like:
Weeks 1 - 4 Osta 12.5mg
Weeks 5 - 8 Osta 12.5mg, DAA/Erase
Weeks 9 -12 DAA/Erase
You can shorten the Weeks 9 - 12 if you don't feel shutdown or just want to end the cycle.
another interesting stack could be osta+formeron what do ya think about this? as a bridge after pct and before a new cycle...