We have been developing iPhone apps for years and while we specialise in Xamarin, iOS is the first love of several of our mobile development team.
If an iOS app is aligned with your market and business goals, we want to be involved. It doesn't matter what size project.
This will depend on your audience (and to some extent your budget). Ideally an app is built for each device, so that's two separate apps for iOS and Android phones.
But this isn't always feasible and there are options to create a universal app, however, if you know your intended customer base or audience uses iPhones, creating an app specifically for that will ensure the best experience.
iPhone apps generate more revenue that Android.