What specialist should I look for to solve my problem?

Question

We have a specific product and now we need to create a cross-platform application. To solve this problem, I'm going to look for a specialist (studio, freelancer), so I'm wondering who and where to look for?

In short, we need a cross-platform browser (based on some browser or written from scratch) that should implement:

1. Registration (+ login) account
2. Account settings
3. Depending on the account, the settings we need should be pulled up (user agent, cookie, proxy, ...)
4. Hardware binding (i.e. 1 account = 1 device)
5. Implemented the ability to pay for a browser subscription

And in addition, a database of customers (date of payment, etc.) and their own browser settings has been created. And at the entrance, his data would be pulled into the browser.

What is the best way to write it, what kind of specialist do we need, what skills should he have and where is the best place to look for him?

Thank you.