I watched a documentary on the War of 1812, and it seems like no one really believed the English would march on Washington. This of course ended up being wrong....
but fastforward a bit, to the Battle of New Orleans. It seems to me that Andrew Jackson had a little bit of time to prepare for the invasion of New Orleans. How did he know that was where the British would go? I mean other than the obvious its a regional target, but it wasn't like he was camped out there since the outset of the war, since he was marching all over Alabama during most of the war.
TL;DR my main question: How did Jackson know the British would assault New Orleans when it did?
Don't have time to go into the full depth of your question but just wanted to point out that there were plenty of high ranking officials who believed Washington would be targeted and not Baltimore or at least in conjunction with Baltimore. Most of the blame lays with John Armstrong(Secretary of War) who neglected to even lay down basic functions for the defense of the city. Defenders of Armstrong usually point to the stringent military budget Armstrong was operating under, but in my opinion this doesn't excuse the neglect of even basic defensive preparations.