should it be invested in bitcoin and hold?
I will choose this investment instead of other investments and also I'll put this in real estate because here in my country it's one of the most profitable investment.
should it be invested in alt coins?
You can invest in alt coins but I don't focus most of my fund there, I'll invest maybe 10% of it and will only choose those reliable coins.
and why or what will make it sustainable via etc vs. alt investment
You should be the one that will sustain your investment by studying the market, it's risky you know.