300 gallons is, like, really big, right? I have a 40 ga and am trying to imagine something 7.5 times as large....
I'd set up a European pond bank with a mossy shore and lush plant life in the water and some wooded back country with a small creek flowing through a canyon in a beech and oak forest. There would be populations of European newts breeding in the pond. There's be slow worms and grass snakes basking on the edge of the pond. In the forest, there's be Salamandra breeding in the creek, and wild boar would come and snuffle in the leaf litter for beech nuts and oaks. Fallow deer, though shy, would be seen occasionally grazing near the pond in the morning light. I'd have a small cabin - nothing fancy, just a modest little home - set up on the meadow by the pond, and all the animals would love me and come hang out with me and I would be a friend to all of them. There would be no cell phones, e-mail or computers. Only soft rain, mild sunshine, and the smell of wet soil and flowers and damp moss......