I have no idea about portable/prefabricated houses. I do have a few of thoughts though 
From a cost perspective, it would be cheaper to build a permanent structure using local materials. The added benefit is one of aesthetics.
Plan and build this structure in a location that will not interfere with the main farm house that will come up in the future. It could be used in the future as a cottage for guests, store/work room etc. or be converted into quarters for farm workers.