The pleasures of gardening, a successful garden season, involves mindfulness, patience,
a healthy appetite for learning, researching and problem solving, and most important...
acceptance.
...and a boat-load of crap and a truck to haul it home in.
It is a bit like wack-a-mole. Once things balance out, one critter dealt with, or disease
solved, another takes its place.
Your plan should work being that small and if you already own the structure. Even the
inexpensive brackets used for saw-horses using 2x4's would work. The top horizontal
support is key for strength.
I've had all the critters and somehow they come and go, but I still have some fencing
for certain things to deal with over-population. Recently the heavy snake population has
sovled most of the critters like bunnies, and the various tunneling rodents.