It just never ends. I'm going to be building out a 4x8' flower area soon. Nothing like what you built though.
I won't be doing it again anytime soon, just too old for it. still have dirt left to spread around from the dig and I've worked on the pile a few times already... my first run yielded about 2.3lbs and a bunch of trim that I haven't weighed. these were 60-65 day autos which some I let go into the 70s. so not bad for 2 months of growing, it should only get better too as i learn.