What you can do is load all the images at once and lay them all over each other. Then manage the opacity of them so that only the one you currently want to see is visible.
You'll want to preload a few ahead; at the moment the best way to do that is set their opacity to something not quite 0, like 0.001... that triggers the loading but isn't strong enough to be visible (especially if it's layered below the others anyway).
With a thousand images you definitely don't want to preload everything at once, so you'll have to be smart about when you preload.
You probably can't do the entire 1000 at 20 frames per second in one shot, just because of the speed of the network.
BTW, to be sure the next image is loaded, you might want something like this (still in development): openseadragon/openseadragon#723
... though you can get away without it.
... and this is the one for a better preloading mechanism than the opacity trick: openseadragon/openseadragon#821