I would try not to fret too much about this. The Year 7 intake at Wilsons is made up of boys from over 70 different schools and most boys enter the school knnowing either no-one, or one or two other boys. The school makes a conscious effort to split friends into different houses to encourage them to make new friends from day 1. They very quickly learn their way around the public transport system. My son (in year 7) is fairly reserved and very scatty, but it took him only about a week to get the hang of the trains, buses and trams (his journey involves two trains and a bus). The Wilsons boys seem to gravitate towards eachother on public tranport and I'm sure he will have a good set of 'train mates' from different houses and year groups by the end of September.
Good luck and congratulations!