These things change all of the time and may vary day by day. The best thing to do would be to check the notice boards when you arrive at the station.
Platform Number 14
The platform on the north side (forgot the number)
Platform 1
There is no such tracking system, which can track exact departure or arrival platform number, actually it decided by station master according to train schedule. At other hand most of train have a fix platform at which train runs, but in some cases like delay or more it can be changed. So its not fix platform all the time for a train.
There is no direct train between Heathrow and Southampton. You will either have to take the tube (underground) to Waterloo and get a train from there or take a bus to Reading and get a train to Southampton from there.
Platform No.5
Platform number three .. (3) .. Ajmeri Gate side ..
the London train station
12 platforms are in regular use.
Yes, it seems to. If you put in a search on the national rail website for trains Waterloo to witney via clapham junction it lists a number of trains.
Yes, from Waterloo Station.
The common nouns in the sentence are: people, platform, train.