I use 4 inch pots for all my droserae species. As to how many plants per pot, hmmmm. It varies from species to species. I would say 4-5 rosetted species like spatulata is about top end. D. anglica: I have 3 in one pot, but I think it would be better to go with one or 2. One D. adelae will soon fill a pot. D. capensis one or maybe two. I think the smaller clay pots you mention are not a good plan, one inch is not suitable as the roots of many droserae species will soon outgrow the pot long before maturity, and the clay absorbs salts which are not good for the plants. In my experience, the deeper the pot, the better the plants grow, regardless of species.
Pygmy species in particular want as deep a pot as you can provide. Don't let their small sizes fool you. In habitat these roots can reach a meter in length or more. For many pygmy species, you need to be able to provide moisture to the roots while the medium at the surface stays dry in order to get them through summer dormancy. I grow my D. adelae in an undrained glass bowl. The rounded sides of the bowl encourage the roots to come to the surface where they form plantletts, creating an interesting "mound" of plants. A couple of observations regarding substrate: both D. anglica and adelae (in my conditions) prefer live moss as a substrate, and very wet to sub-aquatic conditions. I mill the live moss in a blender which restricts its rampant growth long enough for the seedlings to establish themselves. Capensis and spatulata I grow in a typical 50/50 peat/sand mix. Capensis in particular has long thick roots which typically reach 6 to 8 inches. Good luck, and I hope this helps.
Should I be thinking low flat type of pot or taller for deep roots, I really am un certain as to what one does with young plants, lol.
