This can go on for a long time.
We have two little boys that both want one.
But that was enough.
Many colonies failed.
Say a couple of grams worth of nanotechnology self-replicating machinesintended to work on handy asteroids or other free materials lying around the destination solar system.
Send a ship to Tau Ceti and you may not even have an engineer smart enough to fix all nude stray problems by the end of the voyage.
The preparation itself is a multi-century project, and one that relies crucially on its first step succeeding, which is the creation of a sustainable long-term civilization on Earth.
Donnie is a very interesting doberman.