How fast is it travelling as it comes into landing, before and after the re-ignition of the engine, and how quickly does it decellerate??
I would expect that it would be falling at about terminal velocity before the engines begin firing again. Would this be correct?
Each launch is different, so there won't be one single answer. However excellent simulations to literally dozens of SpaceX launches (and some others as well) can be found in flightclub.io and that's where I would turn first.
For example, from this answer one can see an example of CRS-10's F9 first stage trajectory and velocity profile (subset shown below). The orange line in the first plot is the 2nd stage, the blue line is the first stage, in this case returning to the cape. The arrow indicates the estimated location of the start of the entry burn. There are of course also the boost-back burn before and landing burn after this.
In the second plot, you can see all four of the 1st stage burns highlighted in red. The first is of course the launch itself, and ends at the point of separation.
