The Death Star wasn't a great idea. It united the Rebel Alliance and gathered all of the empire's resources into one big fat target. read more
As previously mentioned, the Empire could have produced 6,000 Imperial I and II Class Star Destroyers, or 1,000 Executor class Super Star Destroyers. But the Death Star was a project several decades in the making. The original plans were drafted before the Battle of Geonosis. read more