The wave is both figurative and realistic. As we lead up to the revolution, there is more and more turmoil. The hanging of Jaspard is one of the catalysts to rebellion. Although Dickens may describe the scene with romantic imagery, much of what happened is historically accurate.
Though this scenario seems exaggerated to you and I today, it probably isn't. Remember, this is the culmination of years--decades, even--of starvation, frustration, and anger. These are desperate people fighting literally for their lives and livelihoods. When Dickens writes that "the living sea rose, wave on wave, depth on depth, and overflowed the city," it seems to me a perfect picture of their overflowing of emotions and desperation.
I agree. Many of the stones which the Bastille consisted of were dissembled and used to build other items in Paris--bridges, other buildings, etc. All the statues were taken down and melted to make ammunition and other needed items in time of war. The two quotes you have above are excellent ones to point to the realism of this wave of people who stormed in and destroyed all that represented big government and status that the common man had no part of.
On July 14, 1789, the Storming of the Bastille actually took place so Dickens bases much of Chapter 21 on real life events. In the novel, the Defarges lead the attack and the mob grabs any type of weapon they can find as they charge the Bastille. It is a blood-thirsty, unruly mob that Dickens metaphorically describes as "a raging sea" and "a whirlpool of boiling water." The mob, just as a tsunami, washes over and into the Bastille, beheading guards. This event actually took place, so yes, I would have to say the mob's violence is very realistic. Whenever you have a large gathering of people whose emotions are in control of their reason and they form a mob the violence will be unchecked. When one is part of a mob, one loses his own identity so it allows for man's most primitive, brutal nature to appear.