how much jul or ws studio strobe is enough for my 50 dslr rig in 6m * 6m studio

[sia]

hi to all
i am making my rig and should buy studio strobes for 6* 6m full white painted
 , i want to know for a studio 6m * 6m  , how much jules or ws is needed ?
and  i should set : f 8 or f 11 or more ? for best result
tnx if u guide me