You should (and will) mind algae, since it will get on the plant leaves and eventually kill the plants. Some of those small snails will help, plus not having the light too intense or the duration too long.
Given the intended plants, pennywort and wisteria, submersed and not emersed will work better here. Emersed works very well with bog plants like swords, crypts, etc. Both Wisteria and Pennywort are marsh plants that naturally grow emersed and submersed, the leaf structure obviously changes depending upon this. If aquatic cultivation is intended down the road, submersed cultivation would be preferable.
As with any tank with plants, finding the balance between light intensity and all 17 nutrients is all that is needed. But without fish in the tank, nutrients will be in shorter supply. So you will need to add them somehow.
I have a 20g tank with plants that I keep running as a QT for new fish acquisitions. It can sit without fish for months, longest period being a full year. I have noticed a difference in the plants between periods of fish and no fish, and the plants grow better when fish are present. Obviously this is because of the additional CO2 (from the breakdown of fish waste and respiration) and various other nutrients that enter via fish foods. Substrate is play sand, same as my other tanks (except one), and there are many Malaysian Livebearing and Bladder/Pond snails (these help to break down organics and provide more CO2). Lighting is a basic two-socket inandescent hood using two 10w Daylight 6500K CFL bulbs. I fertilize regularly with Flourish Comprehensive the same as the other planted fish tanks. Plants remain alive but definitely grow more slowly. There is never any sign of algae in this tank.
Byron.
