For instance, if a Jedi Force-pushes something 1000 meters away, is the effect instantaneous or is there a propagation delay, something like the speed of light?
The same as the propagation delay for hologram transmissions; presumably instantaneous
As mentioned in a related question, Darth Sidious once Force-choked Dooku from "light-years" away; the hologram of Sidious and Dooku's asphyxiation were perfectly in-sync, which means Sidious' Force use propagated no slower than his hologrammatic self did.
Since holo-conversations (such as many conversations assorted people have with Sidious, or with Leader Snoke in The Force Awakens) don't generally appear to suffer from any kind of lag, both are presumably instantaneous.
It's not immediately clear whether this would apply to Force abilities other than choking, but there's no good reason to suspect they wouldn't.
It depends on the power
In the films, we see Yoda, Obi-Wan and Leia reacting to far-away deaths instantaneously. There is also the transgalactic Force choking mentioned in Jason Baker's answer. These seem to indicate that there's no speed limit on the Force itself.
However, other powers (such as Force push, lightning, etc.) seem to happen as a "wave" (see 1:43):
So for some powers at least, it seems like there is a delay.
The Force seems to be exempt from all known laws of physics. Awareness of the deaths of the inhabitants of Alderaan was instantaneously known to Obi Wan.
This is contrary to the speed limit placed on everything, that of the speed of light. The example I love best is if the Sun was to explode, vanish in an instant, or otherwise lose its gravitational pull on its orbiting planets, those planets would not suddenly fly off into space.
The lack of gravity would not be felt till the moment the light from the sun stopped arriving at the observation point, which for earth would be about 8 minutes. The gravitational field would stop at the moment light stopped arriving.
Now if a space station was orbiting very close to the sun with many millions on board they would feel it much sooner than those on earth. If they were 1 light minute away from the sun and the explosion killed them Obi Wan on earth would know this instantly but Earth and everyone on it would not know for seven minutes.
The Force effectively transcends space time.