These issues are studied by
NASA in a rigorous manner. This is the reason (one of them anyhow) for the centrifuge project on the space station etc, although the presence of the centrifuge created enormous difficulty with maintenance of the microgravity environment. I am not sure where all that is now and I wasn't directly involved with it anyhow.
The following links cover many of the issues involved. The future possibility of manipulating space itself as a drive mechanism seemed intriguing. At any rate we can calculate the energy requirements if it becomes possible and it isn't cheap. It would require the consumption of one of our largest planets basically. So even if theoretically possible it may never become technologically possible.
Nano technology, when that takes off would be the most hopeful route to surmounting some of the technological issues of utilizing the energy of planets. But consuming a major planet would maybe throw the rest into chaotic orbits etc, so there are massive problems and issues to resolve.
Interstellar travel - WikipediaIs Warp Drive Real? | NASAWarp Drive and Cloaking Devices: Not Just Science Fiction Anymore? - Universe Todayhttp://www.physorg.com/news8817.htmlCentauri Dreams — Imagining and Planning Interstellar Exploration
The problem of not knowing what we'll find in terms of planets to colonize seems one of the bigger issues.
Imagine having come to our solar system without our earth existing.
Mars isn't so bad but what if venus is the best planet available?
Boilogical terraforming would be too slow, but if we master and can control nano technology ala the borg capacity, maybe things like rapid terraforming can become possible.
I don't even want to think about the issues of creating a biologically compatible ecosystem. Talk about complex! We would likely have the capacity to create lifeforms from DNA seeds by then so removing the requirement of dragging along actual species, etc.