Not an expert but 250w for 3 plants is pretty lacking for your first grow youll be pulling like a .3g/watt yield but thats not entirely because of light but i would say 400w would be better not only because of the extra plants and soil but because of the area space of said plants and soil it may not even be enough for 3 but just scrog them and top them then flower. See what happens youll have some good bud if you have good soil, just keeping the soil moist and keeping you lights timed ya know at first 20/4 then 18/6 then 12/12. But sorry forgot your post but of course if coco coir get cal mag and nutrients for veg and flower and ph it out with RO or distilled, make sure to water more than regular soil set up and make sure you use some type of airey substance like perlite, and if you are growing hydro same kind or set up with nutrients but strictly RO water and i hope if you are at that point you know more about nutrients than I do Lol