What happens if I demolish a monument that I constructed

When you destroy the ship itself.

You're off to a good start next I'd get some defenses up, turrets and sandbags to be more specific. This will help with raider waves.

Which brings us to our next part: getting more people.

You can get people in 5 ways right now.

1. People will wander in and just join up no questions asked
2. An escape pod will crash and you will have to rescue the person and convince them to join
3. When fighting raiders, randomly the killing hit won't kill them only knock them unconscious. When this happens you have the ability to capture them
4. The same can be done for visitors
5. The same can be done for the people in cryo-sleep pods. A warning about this one though those pods are guarded by some hard to kill and hard hitting enemies open at your own risk

When you capture anyone you need to have prisoners beds set up for them to sleep in. I usually set these up away from my main colony just in case one breaks out. You then need to have a warden "try to recruit them" your chances are better if the person is not injured and well fed.

As from where to go from there you could outfit people with bionic parts, set up different productions to earn lots of sliver or build a rocket and escape the planet.