I have done several similar types of projects. I often do the same thing. So, your idea seems pretty good.
If space is available I will transcode HDV or XDCAM footage into ProRes 422. If space is tight, I may use ProRes 422 (LT) or leave the footage as is.
Regardless, I will always edit in ProRes 422 or ProRes 422 (HQ) sequences, depending on how much I manipulate the image in FCP (filters, color correction, etc.). I then export the final output to ProRes 422 (HQ), though the standard version may work just fine. Testing the workflow on a small amount of representative media is always helpful.
Anything recorded as H.264 will definitely be transcoded into ProRes 422 (LT) or ProRes 422 before editing.
So, your ideas are sound (IMO).
-Dave