Sorry... the day's coffee is wearing off. 🙂 I didn't read all of your last...
You're correct. Since the rows are going to be added on a onesy basis, there could be some pretty nasty fragmentation at FILL FACTOR 100 on the non-clustered indexes. I don't believe even an 80 FILL FACTOR would help there. Might want to go as low as, say, 60 as a guess. Best thing to do would be to find out what an average day of inserts looks like and calculate a FILL FACTOR to support the inserts.
--Jeff Moden
Change is inevitable... Change for the better is not.