Creating webhooks for multiple clients through an API

[humble_reader]

Hello there,

I want to integrated shopify with my SaaS product.
I want to create webhooks for each shopify client in order to proces their orders in my system.

What is the easiest way to achieve this goal?

Do i have to create public app? If so is it okey to create an app that only puprose is to get access to my clients API?
Can i create that kind app without hosting any shopify files?
Is it better to implement oauth authentication myself or use a gem: https://github.com/Shopify/shopify-api-ruby

Any help will be appreciated.

Thanks a bunch!