Can I get more ground layers? And if so, how?

basic users get 2 items per layer you can use up to 3 ooh la layers per layer. Each ooh la layer gives you 1 extra item in that layer gold account users get 3 items per layer (without ohh la layers)

so the max amount of items in any given HA layer is 6

Gold Account perks include one extra for each layer and add +1 for the layer of your choosing for 31 days.

Using a Gold Account gets you an extra slot in every layer for the time the GA is active; additionally, gives you a temporary extra slot in a layer, I believe it lasts for a month. Ooh La Layers can take you up to...I think 6 slots total? And they're pretty cheap, so they're a good temporary measure.

Oh well c: thanks for the information!