Can I have a folder (on the home screen) with more than the default amount allowed per folder on the Nexus 5, which is 16?
While there are root apps/extensions such as Xposed GEL Settings that will let you modify all sorts of settings in the Google Now Launcher (formerly Google Experience Launcher), folder capacity limits is not one of them. Google's aware that this bothers people and it's a confirmed change in Android M. As the Google Now Launcher is installed and updated via the Play Store, it's not impossible that we may see this update reach Lollipop as well, but if so, we have no way of knowing when.

Your only option, which I know you're not interested in, is a third-party launcher.