The warranty plans for a new vehicle start back at mile zero regardless of when you buy the warranty.
So a 3 year extended warranty runs for the same period as the factory 3 year warranty. if you want to go further than the factory 3 year warranty, you have to buy the 4, 5, 6, year etc ESP plan.
On the incentives, there is $1000 ford money, $1000 for financing through ford and $1000 if you are a current ford owner so that's probably what aggiegrad got to get the $3k in incentives. (that's what I got as well)
That is correct on the incentives; ford cash back, ford financing, ford loyalty.
As far as the warranty, most everything has been said. But to recap:
The warranties run from the in-service date regardless of when you buy the plan so you don’t get it for longer if you wait longer to buy. The benefit to buying during your initial 3/36 is you’ll get a loaner during any warranty service.
You do pay less when you buy it at the time of purchase, but you can get just about the same price for the whole first year.
You can buy the plan through any ford dealer and many dealers have made a name for themselves doing nothing but selling the plans online (Lombardy, Flood, etc). If you go to those websites you can get a generic quote for the term and deductible you want (I did 8 years, 100k miles, $100 deductible). The quote will not be trim specific however, so expect to pay a little more when you give them your VIN and finalize.
Those plans work just like the one you buy from your dealership at the time of purchase.
You can either buy from one of those dealerships online or, as I did and as Brian suggested, use that quote to negotiate your dealer down at the time of purchase. There’s not really anything to argue about; they either match the price or you tell them no thanks and buy on line...you’re in the same position either way. So buying from your dealer at more than the price quoted online is akin to setting the difference on fire.