There is no minimum number of dresses. Just get as many as you will need for a couple of months right after the wedding so you can wear to dinners if you want and around the home. If someone gets 1 dress that doesnt make it the minimum. You should look at your own situation and decide.
I totally agree. You don't need to make a minimum. Fashion changes quickly and unless you're going to wear all those 50 joras within a year or so, you might find that it becomes outdated. For me at least, I don't want a ton because I won't be wearing heavy joras all that much in the States.