In regards to the Falcon firing right away in that "through the TIE window" shot, you are absolutely right that the Falcon WOULD be firing right away. Of course, it could also be true that it took Han a few seconds to line up the target before he fired, but this leads us to another discussion.
When working on BSG, or really when anyone is doing anything on a movie, there is always the balance of what is real vs what works dramatically. For example, if you've seen it, I did the big seqeunce where the Pegasus takes on the 3 Baseships and rams one. There was the very valid question "why would the Baseship just sit there? Why doesn;t it jump or move out of the way?"
Well, first of all, if it jumped or moved out of the way, we wouldn't have our story. But the point was well taken so I felt it was important to justify the action, so my take on it was that the LAST thing the Cylons would expect from humans is that they would ram their ship. They have been protecting their fleet to the death, plus the Cylons didn't know the Pegasus was deserted, so they really were taken by total surprise.
In the case of your shot, I still strongly feel the pacing and grace of the shot are hindered by having all that laser fire back and forth right from the start. Your eye is drawn all over the place and you don't have a chance to feel that moment of dread and suspence as the Falcon is being locked into the sites of the TIE window.
However, you can have everything you want by letting the Falcon get lined up, the TIE starts firing and a half second later the Falcon fires back. It's totally reasonable to assume that it takes Han a second to aquire HIS target. There's enough logic to justify it and I think it would help preserve a wonderful shot from the film that should largely stay untouched.
Remember, I think everything else you've done with that sequence is great - this is the ONE shot I felt should stay closer to the original.