To get the 'track' buttons working, and also the up/down buttons, go to Reaper's action menu (hit the ? key), and in the window that opens, add the action and the key in the little window lower right.
The knobs you can map to track volume etc, but is a bit tricky involving TrackReaControl, see here:
https://www.youtube.com/watch?v=E_7DBXDVZt8 I prefer anyway to map them to the knobs of some favorite synths so I can tweak the sound while playing etc. To assign the knob, either use the synths own built-in 'midi learn' feature, or use Reaper's by moving the knob you want to assign, then click the Param button in Reaper's FX window and Learn there.
One thing to be aware of is that the big square 'drum' pads on the Launchkey send on Midi channel 10, whereas the normal keys send on channel 1. Normally this will not be an issue as most VSTi's (virtual instruments) will play on whatever midi channel they receive, but some might be picky, especially samplers or sample players. (The reason why the pads are on midi channel 10 is from old where drum machines were fixed to that channel).
A great little keyboard the Launchkey Mini. I got one for the kid and a SL 25 MKII for myself, but ended up sending the SL back and am now using the kids for myself..
It's so small and handy between the keyboard and mouse, and also so light to have on the lap.