Questions for the (small) pond-havers

I’m considering whether or not to add a small pond to my wildlife garden – either something in a small container or directly in the ground – but I have some concerns. Hoping people who have similar ponds could let me know about their experiences and maybe answer some of these questions:

How much maintenance is required and how long do you spend on it (time and/or money-wise). Have you had any issues with it bringing in unwanted guests? (rats and the like). How much of a benefit have you noticed from having it? More wildlife, different species, things taking up residence in it, etc. How much has it cost to get it all set up and running?

Thanks!