Replacing bitcoin will be very hard to do as bitcoin is well established by now. As long as the bitcoin foundation takes the right decisions at the right time, everything is going to be fine for bitcoin Nobody can predict the future however bitcoin may remain number one crypto for next few years. 

i have used bitcoin for the buying of ethereum and other altcoins  and now i will pay for online server for a website. Bitcoin will become top digital currency soon  because of a lot of trust in  it than any other cryptocurrency.

 I think it is only applicable if you have advertising a wallet or a platform about of bitcoin  but advertising bitcoin itself is not a good choice But i  believe social media is more popular than television now

People think gold is safe because gold prices are also much more stable than bitcoin in the trading market .
and  that people who buy Bitcoin always have a fear that it's price may drop anytime 

All investments involve risk. But people cannot insure themselves against this. The most important thing is never to put all your eggs in one basket.  I have great trust in bitcoin and I believe it will always thrive as it always has.

Yes it is ; Because it's safe for them . every criminal always takes advantage of what is around them. Nobody Can locate you if you use bitcoin. You can hide your identity. That's why criminals use this as their payment method

Although there different ways to earn BTC 
for me the best way is trading, i know at first you need to have knowledge, make some research about it,
i think signeture bounth and other social bounty will be the great source of earning more bitcoin . but like what other people say dont put your eggs  in one basket.

 It is very risky.  the market of crypto currency is unstable You need to be prepared for any outcome and i wont bet all my asset on Bitcoin. However, I will try to buy BTC more and hold until it reaches new peak