You can look up the Ofsted report on the Ofsted website and the academic results on the DfE website.
Both will give you a lot of detail, although you should also talk to people and look round the school yourself to supplement the Ofsted. The DfE entries now give loads of information - for example you can see the average GCSE grade achieved by low, middle and high attainers, and so on. This makes it easier to sort out schools that have poor academic results but have a very skewed intake from schools that are doing a worse job. You may find reassurance in both these documents. Beware of gossip about the school though - it can go round in circles and be years out of date.
Don't worry about it being a Sports Academy - it will still teach all, the subjects, and lots of people live near schools whose specialism is not the thing that they are interested in. You might find the extra breadth of sport on offer means your son has the chance to find something he would like, which is a good thing in life. And I wouldn't worry about the website either - lots of schools use these very badly, get carried away with PR, just find out the real facts for yourself.
Yes, you will be able to apply for several secondary schools and it is normal not to walk to school at secondary age, many children use buses, trains etc. Schools have to publish admissions criteria (a list of the criteria they will use to decide who gets offered a place and in what order - e.g. siblings, people living close to the school) and they have to stick to them. So look on your local council's education website page - that should either give a list of all the schools or tell you how to order the booklet that lists all the secondary schools and the admission criteria, and sometimes useful info about how many applied last year, and so on
And do this for any neighbouring boroughs as well, you can apply to schools anywhere but many have distance from school as one of the most important criteria, so you will be less likely to get a place at schools that do this and are further away. Some operate a lottery, or have specialist places (where you qualify by demonstrating aptitude in a certain area).
Arm yourself with as much information as possible, and do not make assumptions. Good luck