Bitcoin price trends is upward. It is consistently rising, 2017 is the year for multiple all time high BTC prices and I know it will continue next year.
You can still buy BTC when it fells down a little bit because I don't want to think that it will hit a hard drop. Just feel the market and keep monitoring...
It is up to you. It is not a good idea to buy bitcoin as of now since the price is so high. Buying of bitcoin is good in the past 5 months but for now, it is too much higher that we expected. Yet it is up to you still for buying bitcoin. Since bitcoin is volatile, the price for now can be a greater amount in the future so that you can still get your own profit.