Screw length will vary based on the mount you use and whether you need to use any spacers to get a proper mount. You really don't need more than 1cm of bite so just buy screws that give you about that much into the holes.
I've found that monitors/tvs I've mounted seem to have a metal plate at the bottom of the holes so you aren't accidentally screwing into a PCB. So if you already have screws but aren't sure if they will work I would just thread them by hand and see if they bottom out.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station…