This should help. Since you have 5 x 4 obviously a 250 won't cover that. A 2 x 4 flower room would give you room for 16 plants perfectly.
It's actually planned out as 3x3 area for plants, and the additional room is for a standing fan and for me to walk AROUND my plants lol. Thought it out when I was putting a tiny door on a tiny hidden room thats about 1ft shorter then I am, So I have to kneel squat or hunch over, and with my bad back it's not possible to just lean over all the time.
I can how ever kneel on a pillow or something and as long as I have room (the added 1x1 around the room) gives me space to put my legs
Also I'm a legal self medical grower, they gave me a limit as to how many I can "Legally" have meaning I can only have SO many plants, and SO many clones, and dry weight at one time, etc.
I have to play by the rules that they set so I don't fuck up legalizing it for everyone else here in NorCal! So respectively I am going to stay with my few plants, although I will admit If it was legal I'd build a barn and flood it with a SOG.
Also ty for the response, all the other info was welcome. TY!