Is there a way, before arriving at the station, which platform a train will be leaving from?

Sure. What countries will you be travelling in?

Depends on the country-some times the LOCAl planer tells it (but changes always possibel) often for direct conections it is shown/talked in train 1-and sometimes its not at all and you have to look screens or YELLow pages (white is ARRivals)

Very tight looking conn. is nearly always same platform-other side.

We will be travelling in Switzerland, Italy and France

For Switzerland I recommend you to download the SBB app. There you will have all the information you need about Swiss trains.

@Angelo Where is the best way for information about trains and platforms in Italy?

Italy i´ve manged it with the Trenitaliaapp :) It showed the sheduled platform and 20mins before depature the final platform.