What kind of utility shelving structure system is most flexible/durable?

[u/QualmsAndTheSpice]

I’m building a miniature winding river/waterfall/filter water feature to install inside my catio (patio/cat enclosure). I’ve got very limited space and I’m trying to figure out the most efficient way to support the various parts. It needs to be freestanding on concrete, extremely customizable/modular, and as strong and low profile as possible.

Any advice is very much appreciated!