When dealing with such a hefty amount of money it's extremely advisable to contact an accountant to totally sort you out. 500 thousand euros isn't a small amount of money and your government will try to tax your bitcoin earnings. I wouldn't advise doing it yourself, just get a professional in the game. It's good to do your research and all but if you mess up you could be charged for money laundering and dending on the country you reside in that's not a charge you want to face. Better safe than sorry.