Hi Abz217
The minimum requirements before application can be found
here, but include “five (5) GCSEs/Standard Grades (or equivalent) at grade C or above, including English Language and Maths”.
Difficult to say whether number and type of A levels affects how well you progress, but the tests at the three stages are concerned with ability to learn information, thought processes, personality mainly, not sure what the correlation is.
The interview process varies wildly. My first application was submitted in July 2007 which I failed. Second application in August 2008, and I now have my medical at beginning of April, looking to start July/August 2009. Can be done a lot quicker though depends on college places and application timing. Some others on here have suggested not delaying your application though because NATS cant guarantee they will still be recruiting months down the line, especially given economic climate (not sure how true this is).
Not going to go into detail about the stages, read this whole thread and you will get all the info you could need.
College takes between 6-12months, assuming you pass stuff first time, and depending on your preferred discipline.
shugs