I like the cheap easy building that is portable, and secure. You can't beat the security and to build a shed or anything else cost alot more. I'm in it about 4000 for the container, framing,insulation, and drywall. A tough shed is double that and less secure.
I also plan on moving in the next year and I can call a truck to pick this thing up and move it with my belongings inside and then drop it at the new place. A quick electrical service and some water and I will be back to work.
I have a old room running with 4 lights that are set up side by side like your place and I hate it. I'm only running 1 row of lights down one side and then I will have a 2" walkway down the other side. I gave up on trellis and use tomato cages so I can move the plants around to get to them.
I see any insulation inside that room. Is it inside another building? Those containers really roast with no insulation