This is just my honest opinion, but I don't think any of those Old Republic starships from Episodes 2 and 3 would have been necessary for ANH:R. For one thing, Tarkin says during the briefing that "The last remnants of the old Republic had been swept away," and any vessel from the Clone Wars would be considered remnants of the old Republic. Starships and Trooper army most likely underwent changes for this reason. Also, Episode 4 already has plenty of links to Episode 3. Luke and Obi-Wan's discussions on Tatooine are a good example, as well as the few but comprehensive mentions of the Senate.

And about the Alderaan explosion, I think Lucasfilms did do an appropriate job of it. The explosion should be instantaneous.