I don't think is it good to buy bitcoin this coming 2019 but since you give some tips it might be worth it to buy bitcoin this coming 2019.
Honestly, I just following the movement price last 2014 and 2015 so, 3rd quarter of 2019 I'm sure that bitcoin price will rise up again just like what happened last 2015 and I think more event will come this coming a year.
2014/15 crash took about less than 1 year of decline in BTC price before the recovery started. I believe if BTC were to reach new lows now that we would actually be in a bearish market for longer than that time.
It actually took 13 months. And after that was more then half year of sideways from February to October. Only in October 2015 slow growth started.