Hi Angela
First skip he water crystals, in my opinion they dry the soil. If they dry out they will pull the moisture from your plants. I put a small plastic saucer inside at the bottom of the container, used as a reservoir for water.
For plants there is a very nice variegated bacopa with white flowers. This stuff will grow anywhere.
Lobelia is good in the shade get the up right to use as a filler. Might find a shade loving fuchsia for a thriller.
Check out the data base here.
Those small Wax begonias might be good too. Look for the Cocktail series. They stay smaller.
These would all be a warm weather planting when you temperatures stay above freezing.
