In my opinion, it is not advisable to buy at this time, because the price of BTC may fall sharply in 2019, when other ALT price increases.
I don't think so. If the price of the bitcoin falls, the prices of the other altcoins will also decrease. It may be a better choice to invest in bitcoin instead of investing in altcoins
This is a good step for you Bitcoin at a low price if you have a lot of funds to buy it because I don't have enough money to buy some Bitcoin.