You have 90 days after opening a Fidelity account to deposit enough money into your brokerage account to earn your AA bonus. Here's the link --
http://www.aa.com/i18n/AAdvantage/ea...l/fidelity.jsp.
People have reported in another thread in MilesBuzz that you can effectively use the same money to increase your deposit size at Fidelity by moving money in and out. For instance, deposit $30k initially, withdraw $29k, deposit $28k, withdraw $27k, deposit $26k, withdraw $25k, and deposit $24k. This gives you over $100k in deposits (using just $30k of money) and earns you the 50k AA miles. (By the way, the amounts are just examples of what you can do. I'd recommend doing different levels of deposits and withdrawals, but I don't know if it is absolutely necessary.)
You can then use your other $70k to do with whatever you wish.
The other option is to just put all $100k in Fidelity initially, get your 50k AA miles soon thereafter, and withdraw all but $1k or so and put it elsewhere. I don't believe that I've seen reports that this has cost anyone their already received AA miles.
(As I mentioned in my first post, if you want to pursue BankDirect, I'd be happy to refer you.)