Welcome to the forum.
First, some warning
We plan to wrap/build it into a native mobile app
Take care, that may be non compliant with guideline 4.2, risking rejection:
4.2 Minimum Functionality
Your app should include features, content, and UI that elevate it beyond a repackaged website. If your app is not particularly useful, unique, or “app-like,” it doesn’t belong on the App Store.
In any case, my advice is that it is better, if you have the skills, to do it by yourself. Going with an external developer will make you loose control of your app, likely causing problems rapidly.
And much cost:
$450/month (5400/year) for maintenance, that's a lot
plus the upfront: in addition they do not guarantee that app will be accepted. So you could pay $1100 for a useless code.
that will eat all the money (and much more) than you may get from selling the app.
So it's worth spending even a few more months and go by yourself. And to start use, you can start as individual developer, you'll convert to corporate (requiring DUNS) later.
Just register the app name rapidly on the AppStore to avoid anyone stealing it.