50% seems rather a lot at the moment. I would use 10% to buy right now. Since i do expect the price could go down in a matter of minutes. That's the nature of bitcoin and yes you should be very careful with your money.
i buy 50% at a certain price to have plenty of coins in my wallet, and after that i have another 50% left, but that doesn't mean i use the other 50% at once. after that i keep buying with 10% each time. it allows me to buy 5 more times on the way down. since the beginning of me being a trader i use that method, and so far i can happily say that i have never made any losses.