These are great!
There must be articles about pricing or comparables. Don't sell yourself short and consider making enough of a variety that they can be sold as a package. People might feel like they are getting a deal.
You can even make sets to go along with story books that are in the public domain and sell printable versions to teachers.
For custom orders you can offer a customized face and one customized outfit, and then let people chose the remaining outfits from your inventory. The customized outfits can become new options in your inventory for future sales. You could end up with a varied collection using other people's ideas. Win-win.
I'm not sure if copyrights are the same for paper dolls as art. A tricky thing about commissioned art is that the rights belong to the person doing the commissioning. You might want to research ways to get around this so that all rights belong to you.
I see the potential for a book.