Which is a safe coin to invest in the long term?
How long should I hold it?
Is there a risk that I might lose it all?
I am a noob in cryptocurrencies. Help.

I was thinking Litecoin, is it a good idea?
There is no safe when it comes to investing in cryptocurrency, but in order to secure your money do not invest in the coin which is a newcomer to the market.
It depends on you, you must set your goals/milestone/desired income when to encash all your coins/investments.
Yes, if you picked a wrong coin probably you will lose all your money in an instant, because there are lots of scammers out there.