I want to kind of make my home more comfy and inviting, and I think a koi pond could help make it look unique, too. What can you tell me to figure out if that's the right fit?
A koi pond would be a great way to accomplish that! They can be designed specifically to promote health and growth of the fish.
Is it hard to keep up with? Is it expensive? 
As long as you have a skimmer, water can be drawn from the surface and it will collect leaves, food, and other debris for you.