Depends on your height restrictions, but to fully maximize yield, 4 plants will need at least 5x5 in my personal experience!
You will need an 8" inline fan blowing air outside of the grow room and pulling air out of the grow room as well ran through the same duct-line! I would recommend an air cooled 1000w light and ballast! And gorilla grow tents! Depending on your climate a dehumidifier and or a humidifier may be necessary! An 8 " carbon filter insated ducting is my preference, clamps, also light hangers are great for adjusting light height which helps a lot! you will need oscillating fans for air circulation! One high and one low is my preference! Pots and some premium potting mix like fox farm ocean forest, roots organic etc.
that's about it and you can grow an easy pound! Read a lot about plant nutrition and needs and you are good to grow!