You will have 3,000 bucks in reserve only if the price of BTC does not change. But it is enough for the price to change by only 0.2% in the opposite direction to your expectations and your balance of $9,000 will be completely liquidated.
That is the biggest fear of choosing high margins. OP will use the calculators to determine the profits but will hardly think if the trade goes sideways. Even a small fluctuation will liquidate their account. I have faced this several times and am pretty sure almost everyone's accounts are liquidated at least once. This has taught us never to play with margins.
OP, if you really want to go for a 1:500 account, why not try with minimum balance first? You can give it a try to see how long can you survive. Take smaller trades with small account and multiple those numbers with the amount of balance you wish to trade in future. If you earn profits, for sure try a larger account but if not, try to stay away at least until you see any profits from such high leverage account.