There is a wide spectrum of opinion on indoor ducks, as you know.
Considerations for accommodating an indoor waterfowl include a number of jak2002003's concerns. As far as I am aware, indoor duck-keepers only diaper the ducks when they are wandering about the house or visiting in public buildings.
I would want something to protect the floors from moisture. Accidents happen even in the best setups. Perhaps you can nab some scrap vinyl flooring from a local flooring contractor.
Ducks definitely splash, so the food and water station needs to have easily washable and probably three foot high walls around it, and something absorbent like sawdust pellets in a shallow container underneath. I use the bottom of a large plastic dog crate. Works well for us.
Ventilation needs to be good. When I had three-month-old runners (eleven of them) in our guest bedroom, I left the door open but had a sturdy three-part screen (oh, what do you call those tall wooden panels hinged together???) in place of the doorway, so there was good air circulation.
By the way, we never had an odor problem. I was fastidious in cleaning up. Gold star for me
(Just needed to mention there can be some work involved, but it was absolutely worth every moment.)
You need bedding, that could be straw, shavings, sawdust pellets... that's a decision process in and of itself.
Think about the pathway into and out of their room, for when they go on walks with you. We were limited by an antique heirloom rug in the living room, so we loaded everyone into "The Limousine" - a large portable wire dog crate lined with plastic poultry fence to keep little heads inside the crate during transport - and carried it outdoors.
Bathtime is important, so working that into your schedule matters.
Those are my initial thoughts. A couple of years ago I think it was, Nettie posted a design for turning a room into a super-duper duck room for her indoor ducks. That may still be in the archives.