Custom login app creation - effort estimate

[NativeHealth_R]

We want to create a custom app to modify shopify's login flow

We want customers to be verified and log in using their phone number and otp (we already have an otp service attached to our other website we can use for this)

I'd like to discuss in detail what the effort estimate would be to create and deploy an app like this (we can deploy it on our aws account)

These are the current tasks i see for this project:

- overriding the current login flow to allow the custom app to work

- creating the app menu ui, login flow ui (mostly similar to the existing ui)

- figuring out what settings can be modified from the app settings (and developing that code)

- directing users to this login flow from the checkout/shipment details page (liquid theme code isnt available for this page and there is a CTA for guest checkout that leads to the login flow from the checkout/shipment details page

- detecting mobile numbers of users from our other website and making extra discounts available to these users

Would like to connect and discuss how much time and effort this would take for myself (react developer with amateur level liquid coding experience) or outsource this to a shopify developer who can make it better and faster than we can