CFLs that will give you buds like a HID light cost more than a HID setup.
They are a pain in the ass to cool, pain in the ass to move all the time (and you need a lot of that) and the buds never get as dense meaning much lower yield.
Card board is flammable and rots in high humidity, do you really want to build a box out of it?
It should be hard to track down a closet in the dumpster, or a few doors, or anything you can build a box with a door out of.
You shouldn't care about how many plants are there but rather how much BUD you'r getting.
You can grow a single plant under a 1K light (or 4K light, seen that once) and get a huge yield. You could grow 10 plants in beer cups and get less than an ounce in the end.
With a 150W HID light you should aim to get around 80 grams or semi-dense high quality buds. Shouldn't be hard to get that.
With 150W of CFL you would be lucky to get 60 grams of fluffy as hell buds that is coated to no recognition with trichomes but lacks in potency and taste.
Also look up how many CFL grow logs actually finish with buds compared to HID grows.
I'm still saying you'll be better off outdoor.
Have fun with that info and whatever you decide to choose