The faucets's advice seems good to start but the earnings will be really tiny and cex.io isn't +eV at the moment.
Both faucets and cloud mining are horible bitcoin related investments. I would recommend against them both. If you "invest" in either of these you will either lose your time or your money (or both).
To begin with do not invest everything. And invest it on something reputable and trustworthy
If I have 5 BTC in my wallet. How much should I invest. For example I want to invest it in a gambling site?
I suggest not invest in a gambling site.
but can using to trading.
Trading altcoins is very similar to gambling. If you wish to "invest" in the bankroll of a gambling site, this may be a good idea as long as the site you are investing in is reputable enough so that you are confident they will not run away with your bitcoin