Help needed with soldier who was later private in RFC and RAF in WWI
I have been looking into my great uncle William (Bill) Henry Grant (born 1880 Soho, London). I know that he was a soldier in the Royal West Kent regiment from 1899 and have his attestation papers. In the Royal West Kent he rose to be a sergeant and was a PT instructor. A later search revealed that towards the end of his military career, after fighting in The Somme in 1916, he joined the RFC, the Royal Flying Corps and later the RAF. Weknew nothing about this. I can understand some of the words and abbreviations on the forms but can anyone translate what the various abbreviations and number mean from the clipping below. I can identify the School of Air Pilotage which I believe was in Wilshire but I can't work out what all the other abbrevations are. Another page lists the medals he received which are The British War and Victory medals I assume, but can someone tell me what the writing after they are listed, in two lines, means. Also can anyone tell me how/why were soldiers picked to join the RAF and why Bill was a private in the RAF while he had aben in sergeant in the army? Also the best place to find out more information about the RFC/RAF during this period of WWI.
Also I have two photographs of Bill in the army shown below. Can anyone tell me what the two medals he is wearing in the first photo are likely to be (Bill is second right, second row from bottomn, with another soldier's hand on his soldier). I think this photo dates from before WWI, possibly as early as 1901. And tell me anything about the unform and which regiment her might be in in the second picture which was taken years later when he was clearly much older.
Thanks.