There is no point in burning out quickly. Burn sustainably.
> The world needs a lot of help.
With great power comes great responsibility.
There are many people even in developed countries[1] who need help of those who made it through.
[1] http://slatestarcodex.com/2015/12/24/how-bad-are-things/
You will find a lot of meaning and joy in giving, in focusing on the well-being of others. Your own well-being will follow.
Yes to 3, 4 and 6! 5 Never hurts.