Personally with that small of a space and using 250w hps, I would prob go with about 4-6 plants, maybe 2gl square pots and start flower when they reach about 10-12 inches, cause their going to atleast dbl in size so its always better to play it safe rather than outgrow your space. Hopefully you got some indica dominant plants, do some lst (supercropping, tie downs) to fill out the space, maybe even go with 2 or 3 plants in bigger pots to give them more room to do their thing. It seems like this is the first time your using this space so trust me the last thing you wanna do is have those girls out grow height wise, after your first grow you should have a better idea of the optimal amount of plants to maximize your yield, but personally I would just go for pure quality rather than worrying too much about yield when dealing with that kinda space. Figure out some sort of ventilation, cause during flower its gonna get rather hot and humid, so your gonna want some fans, hopefully some sort of exhaust and a small mounted desk fan and if smell is a factor then you'll need a carbon filter, which you can jimmy rig one up yourself, I'll try and find this link that shows an easy diy method for about $40 rather than spending a grip. Anyways I would shoot for a few short bushy little bitches, but you could always go more plants and lollipop them or let them go all natural, I would just make sure to start your flowering in probably about 2-3wks depending on how vigorous they are. Hit me up if I ccan help with anything, best of luck, peace brotha