I went with 2x4 mostly because you can't get to the plant in the corner in a 3x3. Four plants staggered in a 2x4 works really well with two rectangular lights hung at an angle.
Mystery bean! Those are fun.
I loved the Bruce Banner I got from.. somewhere. Who remembers this stuff. It always grew a tank of a plant and every third or fourth produced this outrageous strawberry flavor I've measured everything against since. Watching for those!