Yes, 24x36 or 30x30 are preferable. I also prefer actual 1"x1/2" cage wire for the bottoms, the wire thicker and better for their feet than hardware cloth, but their droppings will pass through the 1/2"x1/2" too.
Some rabbits will chew on anything that they can get a hold on with their teeth...
Oh, yes, some will chew on those 2x4s that are directly under the wire.
Rebar is all I can think of for support too. My bigger metal cages have wire bars that look like thick welding wire for supports.
I actually prefer the premade metal cages for my rabbits- and when I kept them outside (now they are in stacked cages in a shed with my cavies) I just did a wood enclosure around the cages. Less wood for the rabbits to be able to destroy and poop on. (I don't know how long those 2x4s under...