I've ran hydro before but only on an 8 plant stealth scale so while I assumed the time-to-harvest and whatnot would be similar on a larger grow as well. I was mostly just wondering if there was any sort of increase in efficiency or any other notable advantage that manifests itself on larger grows that I wouldn't be able to foresee.

I'd much prefer to stick with soil.

How much yield could I expect off an 8 or 16 plant grow with a 600w HPS in the same space? I've got 4 now but with only the 400w light and I'm giving them more veg time to help fill up the screen and give them a chance to bush out a little bit before flowering them so numbers should be substantially different.

The only reason I don't have a proper co2 system yet is the cost, not to mention it's easy as fuck for the cops to trace the sale/rental of co2 tanks and it's slightly conspicuous trying to get them from a compact sedan into the house. How efficient is the sugar/yeast/water method of enrichment?

Also, if you had to use cfls for lighting the mother, how many and what wattage/bulb is best?