Recommended: the "Container Atlas" / Handbook of Container Architecture, among others by the architect Han Slawik, who has been repurposing the freight container as a basic module for shell construction since the 1990s.
With all the visionary ideas, do not forget that construction takes place here in Germany. The Energy Saving Ordinance and the entire catalog of building and planning law requirements for a construction project must be taken into account. Even if you want to expand or add on gradually, the entire project must be thoroughly planned, applied for, and approved from the outset.
Shipping containers, especially the 40" containers, are offered new, but more often in damaged condition at low cost. Added to this are the not insignificant transport and assembly/foundation costs, provided that delivery of a 40" container is even possible at the respective location. If the mobile crane is used for a long period, it generally becomes expensive.
The entire expansion including the necessary insulation and building services should cost in the best case about €700 to €1,000/m2 NNF, with very low demands on the equipment. It can be cheaper with predominantly own labor extended over a long period.