Another thing to bear in mind is that that NATS applications are currently closed until May.
Think of starting with NATS as starting a job straight away, you're employed from the outset and you're just on an extended probationary period
If you're successful with your training then you're guaranteed a job with NATS - it may not be exactly where you want, but if you're serious about being an ATCO then that shouldn't be a massive problem.
Assuming best case scenario, if you were to end up at Swanwick, you could expect to validate 2 1/2 years after starting at the college. That assumes you pass everything first time and don't hit any bumps on the road through live training. Plan on at least three years in reality and then anything better is a bonus.
You wouldn't be able to stay near Stansted either to train, all NATS training is done at their college in Whiteley, just to the East of Southampton. So you'd either be uprooting the family or commuting on a weekly basis to start with, which is not to be recommended. The training course is intense and having a long drive isn't going to help you. That said, people have done it and passed so it's not insurmountable. After the initial training you'd move to your unit which is wherever NATS decide to send you, anywhere from Scotland to Southampton and most places in between.
As others have said, it's a rewarding career when you get there and almost a job for life.