30btc is enough. because btc price after 20yrs will boom. hhaha
You can never tell because all we can do is to speculate, if you believe it will happen, you are free to invest and even put your life savings on bitcoins.
Thats true no one knows how long the life of bitcoin or even it will last forever and also the price will be unpredictable but i think if the price would be stable in 20years your 30btc is not enough to make your life happy.