Humanity's future in space

When I was a young leader in the United States Army almost every one of my soldiers just wanted to finish their first enlistment and get out. I would sit each one of them down and tell them that if they want to get out they better plan to stay in. What that meant was the steps that would ensure success in transitioning out of the military happened to be the exact same steps that would ensure success and promotion within the military.
I would like to now share this message with humanity. If getting off this planet and colonizing the moon, mars, or anywhere in space is the goal then we must first plan to stay here. The steps we as humanity need to take in order to successfully reach for the stars happen to be the exact same steps we need to take to successfully remain planet bound for the long term future.
The conversations that happen around this topic need to be paired with action and those actions need to be happening at a much faster pace than is currently happening. How many people will be needed to ensure successful colonization in space? Do you know? That is the starting point. Would all those people be traversing space in the same ship? Talk about an "all your eggs in one basket" type of scenario! If the answer is no, which I think it is, then how many ships would be required in order to venture out into the unknown?
Looking at these two questions gives us a good starting point to begin taking actionable steps. Those steps are part of my goal over the next three years. First though, I really want to hear your thoughts and opinions.