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.