I like cypress for all outdoor wood applications. Cypress is resistant to rot. Trees grow from a rhizome which makes them tightly packed causing straight trees. Which produces straight lumber. We in the Southeast US have cypress local.

I go 100 miles to a mill when I need cypress. Much different experience than home depot. And greener. A much smaller carbon footprint then home depot. And according to the mill owner the trees replenish faster than they cut it.

For shelves get aluminum or metal that is protected against rust. The fertilizers are very caustic on unfinished metal.

Most of my orchids are in pots that are in hanging wooden baskets. That improves air circulation and it is easy to move around.

I have plastic Dura-Bench tops:
http://www.greenhousemegastore.com/product/dura-bench-plastic-benchtop/bench-top-material
I made simple Trex frames and legs to make interlocking and easily moved bench modules. They're rigid and won't warp, and will never rot. I love them!