Creation of dynamic site collection and sub-sites

We are having an enterprise system where organization wide operations are maintained. Recently we decided to provide collaboration features for each operation maintained in the system using SharePoint 2013, since that enterprise system did not provide any social/collaboration features.

Assumptions/constraints -

1. Every year 2500 operations are created
2. Each operation can have documents and other content scaling upto 5 GB.
3. Only SharePoint provider hosted apps are allowed to build the solution

For seamless integration, we are creating an automation component which will a SharePoint provision site automatically when an Operation is created in the enterprise system (we will get the trigger through web services)

Proposed solution - 

After going through Software boundaries and limits for SharePoint 2013, I'm thinking of proposing this architecture -

 1. A windows service will be created which will accept the trigger to create a site and take care of provisioning the entire site 
 2. A maximum of 700 sites will be created per site collection (based on the size calculations and keeping some buffer)
 3. Once a site collection hits 700 sub-sites, a new site collection is automatically created for provisioning the new sites
 4. Provision the apps and add them to site pages using powershell/CSOM

Kindly let me know if this approach is effective or any major road-blocks we need to take care of in this.

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