Invest as much money as you can lose without much worrying. Bitcoin is about high risk high reward. Bitcoin will rise few thousands from now on and then drop again. It's normal and will it will keep doing it. But in long term bitcoin will reach 30k or more. Alot of experts speculate that bitcoin will reach 50k by the end of 2018. While bitcoin is dropping you can invest in Altcoins and wait till bitcoin is on the rise again. All of this needs time, so it's like a job. If you can invest time, money and nerves go for it. Good luck.