Alas, even given a reasonable form of interstellar travel for human physiological constraints, the chances of finding a target planet with an oxygen atmosphere but no pre-existing biosphere is very low. And the question of human food chain compatibility with alien biospheres is ... well, there's a very good chance that they would find us crunchy to snack upon, rather than vice versa. (I'm thinking at a microbiological level. H. G. Wells hit the hammer on the nail with "War of the Worlds" in more ways than one.)
The idea of finding a ready-made habitable planet somewhere out there isn't science fiction, it's pure fantasy.
You don't colonize the new world by paddling across the Atlantic in a dugout canoe with a few of your friends, expecting to rent an apartment in midtown Manhattan. We have a lot of work left to do on this planet first.
