Which do you want to be? A seedbank? A breeder? A breeder with enough sellable strains that you become your own seedbank? All have different answers with regard to how to do it, but based on your question about rooms, it seems like you want to become a breeder, not start a seedbank. You would require year upon years upon years upon years to get the the stage where you could open what would be considered a seedbank, but selling just your own strains.
What do you actually mean by rare opportunity? If you want to open a seedbank then you open a seedbank. Is this opportunity as in the wife just left you with the kids? Or opportunity like some guy down the pub just offered you 50% of the harvest to be his fall guy in a grow house?
As others have said, most importantly really, where do you live?