I have had up to 8 but i found that you will get just has much by growing 2/3 plants let them veg for longer and you will get just has much yeild,If you are going to do around 6 plants make sure that they are a nice short bushy strain.I'm not saying you won't get a decent ammount i can just about make one crop last till next is ready.I started with one now i have a nice little thing going i have a small room with 4 of them energy saveing lights in you know the ones the ones with 3 u shaped lights on each fitting each 1 is the same has a 75 watt light bulb but they use very little electric iuse this room for my clones.Then i put six clones in the first room for 3/4 week then i put them in room b the other room i have a second 250watt light in.Ialso keep a couple of mothers trimmed short till i need some clones but its a constant turnaround.good luck you are not born with luck make your own save £50 out of your first crop and you will get light and ballast bulb for 50/65pound you your first crop has outlay to exspaned.good growing