There's nothing wrong with someone starting out in a profession and wanting to know where he might be best placed in the future for pay, lifestyle, etc! Indeed, much better to get the question from someone who has at least got through a few hurdles and has a start date. The chances of validating somewhere (not necessarily at the first unit of posting for some, and admittedly it used to be the case that area trainees had an aerodrome rating to fall back on - quite a few of my colleagues at my first unit had been to area or TC first) were close to 50% back in my day, for those who got through the front door of the college. Someone who hasn't yet been through the testing day would have had about a 1% chance of validating....
Anyhoo, can't help you with NATS pay these days but regardless of what some of the doom and gloomers say, some people do get their first choice of posting. I did! It's not common though. A simple way to help is to phone the Manager ATC of the unit you'd eventually like to join, and ask for a visit. I did!
Good luck with your training. Don't forget to have fun while you're doing it.