I have a A1. Am looking to pick up a second cam. Considering, HMC 150, EX1, Z5U.
And the XH-A1S.

I want to go tapeless (HVR-MRC1K or Firestore are being considered too) but am in the middle of a doc that's been going for 2 years. So I have a lot of footage.

How difficult is it matching footage from different cameras is my question and am I being silly thinking about adding a new different cam while in the middle of a project that will shoot through the summer?

I'd get the XHA1s and stick with tape. Why do you want to go tapeless for a documentary where you're going to shoot hours of footage?