That's actually pretty impressive sleuthing.
I'll say. The language that sticks out to me is "you shall be rewarded." Not a smart promise to make to Littlefinger as I am sure he will collect the debt. Could Sansa become Lady Baelish by the end of the season? If so, I fear for Rickon's safety.
So, do people like live in the Vale? All it seems to be is that castle, and the crazy tribes around it.
The Vale is basically the entirety of the Northern East Coast of Westeros. It is probably the third largest of the Seven Kingdoms. According to the Wiki of Ice and Fire (which cites to the officially published Game of Thrones resource book), the Vale is capable of raising approximately 45,000 soldiers.
It is also important to consider that the Vale is the only one of the Seven Kingdoms that has not been swept up in The War of the Five Kings and the turmoil surrounding it (Dorne also, based on the books, but not in the show). In the context of the show, the Iron Islands suffered heavy losses in the war and is in a state of political unrest due to a coup. The North is falling apart under the reign of the Boltons and suffered all kinds of losses from Robb's failed rebellion. The Westerlands have been in total disarray since Tywin's death and suffered heavy casualties in the war, same with the Crownlands. The Riverlands (which already suffered a ton of casualties by taking part in Robb's war) is currently under siege, fighting a civil war against Walder Frey and what is left of the Lannister's army. The armies of the Stormlands were crippled by Tywin at the Battle of Blackwater Bay and what was left was wiped out by Roose's army when Stannis attempted to invade the North. The Tullys/the Reach suffered losses in the War of the Five Kings by supporting and fighting alongside the Lannisters. Beyond that, the future leader of their house is being held prisoner by religious extremists and they are facing conflict with both the Faith Militant and the Lannisters. Finally, Dorne just suffered a violent coup d'etat and is in a state of political upheaval.
The only region that has maintained neutrality and whose armies are healthy, full, and well-supplied are those of the Vale. Beyond that, the Vale's armies are comprised of natural warriors who are well equipped to handle fighting in the winter due to the fact that the Vale is a rugged, mountainous terrain. They are used to adverse conditions. The Vale is currently the strongest force in the Seven Kingdoms...just as Baelish intended when he poisoned Jon Arryn, set all of the other houses against one another, and manipulated his way into control of the Vale.