A database server is your best bet, any XML persistance is inefficient for large user base and definitely non-scaleable.
SQL server is a common approach but NoSQL like MongoDB is pretty trendy right now with low learning curve and high performance.
You should consider using Flex with builtin support for REST web service, manually crafting Http Request is tedious and time consuming in AS3.
Start setting big goal and strive to be better person everyday. Your ultimate goals in life should be:
1. Perfect health
2. Financial independence
3. Great relationship with people around you
Finally happiness is a state of emotion and emotion in many cases does more harm than good. Mastering emotion with your mind and pressing on no matter what life throws at you is what you should really wish for.
1-Happiness is not (and mostly can’t be) a result or consequence , it is just a process. It will come and go, come and go and so on. Almost everyone experiments those “not positive” feelings, so welcome to the biggest club in this planet. But it is completely on your hands (your thoughts) , to make it stay longer and longer with you.
2-Stay away from negative people
3-Be grateful for everything you have (for example, you have a job that you can make a living almost any part of the world, and the only thing you need will be your talent, a laptopComputer and web)
4-Do not ever compare yourself with others.
5-Share your time with your beloved ones.
6-Watch out for every single word you say, try to be always positive ; this will not happen in 1-2 months, but make it a life-style , you’ll see the benefits and it will be worth it.
7-The list goes on, topic is deep, may sound weird but it is all about Science (Quantum Physics) , THINK POSITIVE !
8-Take THIS MEDICINE every morning before breakfast
And remember whatever circumstance you are facing, there is worse thing somewhere else in the world (think North Korean), be thankful and decide to be always happy.