Galaxy Class Ships have included: USS Galaxy (Conjectural Prototype), USS Yamato (Second ship, Destroyed in TNG "Contagion"), USS Enterprise-D (TNG, Destroyed, ST:7), USS Odyssey (Destroyed, DS9 "The Jem'Hadar"), USS Venture (Appeared in several DS9 Battle Scenes along with at least four other unnamed ships), USS Challenger (Chased the Delta Flyer in an alternate future, VOY).
The TNG Tech Manual says that there were 6 ships in the initial production run, plus an additional 6 produced as just spaceframes which were then put in storage. It is likely that they would have been completed and put into service after Wolf 359 and if any remained they would have been put into service during the Domminion War. Additional Galaxy class ships would probably have been built from scratch.
Even with their limitations in battle, they have cavernous shuttle bays and could be used as mobile starbases. With all the space on board, a battle oriented Galaxy Class could fit a LOT of extra waepons by cutting back on the living space and labs. They would also serve well as transport ships as they can carry over 3000 people (normal crew for an explorer mission is 1000, they could probably operate in battle with fewer than 150).