How many plants you advise per m2 when planting indoors?
Alchimia Grow Shop
You can use the SOG technique, with around 25-30 plants per m2. A nice system for intensive growing, but has some disadvantages: if you are caught by police, you'll have lots of plants, and that's something all judges dislike.
For me, it is much safer using the SCROG technique or similar, with few plants (9 at most) per m2. While it is true that you lose some days with extra growth, the grow is much easier if you have to care for 9 plants rather than 30, yields are usually better and your position is much safer.
Notice I'm telling you this while I life in a country where the number of plants is not important if you're caught. If I lived in a country when the number of plants was significant, I would probably grow 2-4 plants per m2.
Hope it helped.