En realidad en ningún momento se ha hablado de manera oficial de un número exacto o aproximado de planetas o localizaciones, lo mas parecido al respecto son estas declaraciones recientes de Casey Hudson en el podcast:
"There are literally hundreds of things out there for you to go and find and interact with. And about 10-15% of those are landable planets or locations that you can go walk around in, drive around on, explore."
Respecto a la cuestión del tamaño a ocupar y su posible cabida en un único DVD, declaraciones de el mismo también, esta vez en su blog en IGN:
Does “Mass Effect” fit on one disc?
Yep, but just barely. This is a monstrous game. In fact, there was a time – not too long ago – when we pretty much scoffed at the idea of fitting onto one disc. But, there’s an art to optimizing the data that goes on a disc – plus we have a few programmers that seem to pull off magic tricks right when we need them.