Would i have to pay for my own flight training?
The only people who don't pay for their own flight training these days work for Her Majesty.
You would never work your way up the ladder from check-in agent to pilot, it doesn't work like that.
You can work your way up the career ladder on the ground, all the while paying for your flight training, then once qualified apply for jobs as a pilot, but you would never get promoted through the ranks.
Check out the wannabe's forum for more info on flight training.
The experience that you gain in working on the ground will be invaluable when you get tot he f/deck and will IMHO make you a better all round pilot than those who have never worked on the ground.