The 5 factory per pole limitation is defined at ../countrol.lua line 149
if #pole.neighbours.copper == 5 then
pole.surface.create_entity{name = 'flying-text', position = pole.position, text = {'electric-pole-wire-limit-reached'}}
return
end
You can change the constant to any number you'd like or remove this constraint entirely, although I can't guarantee no side effects from this change. Since I don't understand why the author would impose this limitation in the first place.