The best galaxy colonization plan is something like seeding star systems with programmable matter in the form of microbe Von Neumann probes The biological ecosystem bootstraps itself into sufficient information and energy complexity, meanwhile terraforming the planet. Then, you send colonists as packets of information in a giant laser beam that takes over the body of the best life-form for inhabitation on that planet. You could perhaps also tweak evolutionary paths through lasers over time to get a good body plan. The colonists don't have to experience any subjective travel time and live inside of containers ideally suited for their local environment in a now-terraformed planet.