_stefano_ , I have one experience germinating and growing Nicotiana rustica; what I did was put about 40 seeds into a Viva brand paper towel, then I wet it, put the paper towel into a ziplock style bay or similar (not fully closed). Put the bag onto a heat mat designed for seed germination, and re-moisten paper towel as needed [with a mist or light spray].
After mine germinated I put them all into the same large container, and covered them with soil; later, I seperated them into Styrofoam cups; they flowered when about 2-2.5 feet tall under constant light.
Each plant didn't produce much leaf mass, but did produce a good number of seeds.
That being said, if you smoke tobacco, germinate 40-200 [the more the better if you smoke usually], and seperate them into their own containers early (if you put them into soil together), because the root systems will be very fragile, and the seedlings tend to be inclined to lean; mine kept leaning in the cups, but were ok under strong enough light (fluorescent ...432 watts).
The ones I grew were nitrogen deficient.