can't help you with a lot of those questions, i'm afraid - wouldn't be sure of the accuracy of my answers!
try going to visit atc units - both nats and non-state to get some or all of you queries answered -
as far as i am aware though nats is still recruiting like mad so even if you are above the age limit - they may take you on after you have selffunded - but don't quote me on that one - 'cos not certain if that happens with folk with no previous experience
good luck with what you decide
prof