If you set it up now before buying the next fish it will be cycled and stable. I make a point of not messing with the filter in my QT once it's up and running and I do a 1or 2 gallon WC a week IF I have a fish in it. Otherwise if it's been sitting a long time with no fish I do a 2 gallon W/C just before buying my next fish.
You are right, daily W/C's are stressful to the fish especially if it's sick and living in an uncycled tank. You need to be patient and let it cycle and stabilize and then everything will go smoothly. And your fish will thank you for it.
