Pretty much the question above. Today I visited Thomas Stone’s house, a signer of the Declaration and wondered just how secret these deliberations on Independence really were.
Maybe I’ve got my timeline a little off, but after the Declaration they then decided they needed to raise an Army. Seems backwards to me. Wouldn’t you want to get your Army ready first and then declare independence? I mean, you’re essentially asking for a fight with the most lethal Army in the world and you don’t even have an Army?
Consider a few things:
One, by September of 1774, all of Massachusetts outside of Boston had already expelled all British power from the area without any bloodshed (see The First American Revolution by Ray Raphael, 2002). The events at Lexington and Concord five months later (April, 1775) were the British attempts to invade and retake the territory that they had been peacefully removed from. By the standards of the day, even though the events of 1774 had not been outright warfare, the rebellion began at that time through the refusal to obey Crown authorities.
Two, an action such as writing, signing, and publishing an announcement such as the Declaration of Independence might be a necessary marketing tool to alert people that an army is needed in order to drum up volunteers.
Three, the timing of the Declaration and its contents suggest that explaining and legitimizing the rebellion which had already been underway for two years at that point was a major factor in its creation and publication. The rebels needed to portray themselves as "the good guys" in order to help gain outside assistance, which influenced the alliance with France in 1778.
Four, the time that transportation and communication required in the 18th century was massive. By the time the Crown in London had heard about the Declaration, approximately a month would have passed since its announcement, since that's about how long it took ships of that era to cross the Atlantic. Then the British government would take some time to compose instructions to their officers in North America, and after they had been composed they would also take a month or so to reach across the ocean. Assembling troops and ships and supplies to then start a campaign across the 3,000 miles of Atlantic Ocean between the land masses adds additional time to this scenario; messages have to be sent to the troops and people who possess the supplies and equipment, they have to travel to the staging areas, then wait for ships to board, load everything onto the ships, and then take another month or more to actually reach North America. Realistically, the signers of the Declaration knew they would have at a bare minimum at least two months until they would have to face larger portions of the British army, and that is assuming that the soldiers were assembled and ready to depart on the docks as soon as word of the Declaration reached Britain. This situation means the signers of the Declaration have exactly the same amount of time as Britain to assemble military forces plus two months of travel time that the North Americans didn't have to spend since they were already physically present on the continent.
Five, the official founding date of the US Army is June, 1775, a full year prior to the issuance of the Declaration of Independence. It might not have been as large and impressive as the British army of the same time period, but it did exist.
So, to address your question a little more directly: yes, logically, one would want to have their armed forces and logistics properly in place before one issues a challenge to a great military power. In this case, however, there were quite a few factors that contributed to this piece of statecraft being written, signed, and announced before an equal or superior military force could be assembled. :)