|I have a two part question. I have a 16|
|Adding gravel to the bottom of a planter is not a good idea. If the planter has drainage holes, no gravel is necessary. If the planter does not have drainage holes, I'd recommend planting in smaller containers (with drainage holes) and setting those containers in your large planter. This way you can take the containers out to water and replace them once the excess water has drained.
Some deer resistant plants for you to consider include Astilbe, Cransebill Geranium,
Epimedium, Foxglove, Lamium, Lamb's Ears, Monkshood, Peonies, Pulmonaria,
Silvery aremesia, Solomon's Seal and ornamental grasses of all kinds.
Best wishes with your garden!