Need advice for my first app development

[lgs]

Hi,  

this is my first experience with Shopify app development. I am creating a public embedded app. 

What I've got so far:

1. I've been able to create the app locally on my laptop (just a static page mock-up for now)
2. serve it via nodejs and ngrok tunneling
3. authenticate it on shopify with koa-shopify-auth
4. create & register the app in my Shopify Partners account 
5. then installing the app on my test/dev store

What I need to build:

1. the customer buy/check out a digital product
2. the product is a private page on the merchant store, hydrated with data and charts coming from my server app
3. the check out need to create the user on the fly and authorise him to access the page he just purchased
4. the user can subscribe for monthly plan

So for now I've the base app infrastructure but I'm not sure how to proceed 

Any advice would be appreciated greatly

Thanks in advance

lgs