Large Terrarium Help Please?

[mariearound]

I was recently gifted an incredibly large glass tank! I keep two species of snails and have been gradually increasing in tank size as my snail interest grows, but this tank is about 3 ft long, 2 ft tall and a 1 ft deep. Although I do plan to keep snails in it, I want to only keep a few in order to preserve the plants. I hope the main focus to be the live plants. 

Does anyone have experience with a terrarium this large? What plants and animals do you recommend?

I am thinking I should do a rock and activated charcoal bottom layer, clean soil in a thin layer and then top with coir and moss. 

Thanks for any advice!!