in that space a 600w would be nice. if you can make the cab 7' do it the taller the better really. prob best off just painting the inside white for now. you will need a carbon filter and spriral case fan preferably a better output fan to your intakes humidity i find easy, cheeky really lol i got a humidity gauge and i control it with a bowl of water or a bowl of salt checked twice a day. salt reduces humidity whilst a bowl of water increases. or if your posh get a humidifier. pretty important to have a good quality timer to run your lights on, (i've had ones which stick on) and another to run an osccilating fan inside the room 15mins on 15 mins off or on all the time like i do. keeps the mould at bay and helps with even temperature distribution