Interesting read and ideas.
IDK how practical it is to build a 15,000 gal tank that can be moved. I mean picking it up with a crane, perhaps driving too, could pop all of them window-to-wall seals, hence, one would need to way overbuild the tank to be able to withstand crazy sheer and deformation stresses, likely having an extremely fortified platform. It won't be "just a shipping container" anymore. Windows would need to be encased in metal frame and sealant front and back, not just front or front and sides, etc.
Anyhow... my 45'x14'x5' rubber liner pond with a 45' window took me about a year to build and very roughly
~$1000 in wood and plywood, screws, etc.
~$2000 in acrylic sheets
~$2000 in acrylic glue
~$1000 rubber liner
~$500 in misc. expenses, Dow 795 sealant, stainless steel bolts, etc.
In sum ~$6500.
Caveats - my aesthetic standards are low and long-term performance of the build is yet to be revealed.