Question about USB storage for this game

Question 1: What is the EXACT install size of Disc 1 AND Disc 2 (especially Disc 1, since we know Disc 2 is 8GB)

Question: Can I play Halo 4 if I install Disc 2 to a flash drive and disc 1 to my 20 GB 360 HDD or do both discs have to be installed to the SAME storage option?

Let me know, thanks!