Found something: according to wiki (yeah, I know…), the opening scene takes place 6 years after the foundation of the Empire/end of the Clone Wars/the Jedi purge (http://starwars.wikia.com/wiki/Rogue_One:_A_Star_Wars_Story).
I think your edit is very fine for the purpose you intended it to be (and the little trims over the cargo pilot character that remove his Jar Jar behavior are definitely most welcome !), but I would suggest (if you are thinking about a v2 for your edit some other day) a slight rewrite of the crawl. Here ismy suggestion using yours with small alterations:
Founded at the end of the Clone Wars, the GALACTIC EMPIRE has spread its evil reign across the Galaxy. Hope and freedom are fading into darkness.
To resist it, the last remnants of the REPUBLIC have formed an ALLIANCE. Little do they know that the Emperor is building a new weapon that would secure his absolute power.
Director Krennic has just located the whereabouts of defected scientist Galen Erso, whose knowledge is crucial for the completion of this super-weapon and the fate of the Galaxy…
(english is not my mother tongue so I take it’s no De Palma quality 😃)
edit: by the way, is there a version of your edit with a 5.1 sound file ? (the bluray version is 2.0)
“I have to say that I felt George’s group of six films had more innovative visual imagination, and this film was more of a retrenchment to things you had seen before and characters you had seen before, and it took a few baby steps forward with new characters.” - James Cameron about Episode VII.