sharepoint enterprise – Automatically generating pages when subsite is created

Migrating from Sharepoint 2010 to 2019 (On-Prem, Classic UI) and I need to implement a solution that automatically generates pages (3 for example) when a subsite is created.

An example would be subsites and subsite pages for departments in a business:

EX: If I create a new ‘Finance’ subsite under my root site and set the page layout via a terminal command, the solution should automatically generate 3 pages under that subsite in addition to the /default.aspx page: a ‘People’ page, ‘Overview’ page, and ‘Contact’ page. Each would use a custom layout set via a terminal command.

Am I looking for site definitions? Or a module (as described here)? I’ve poured through Microsoft’s documentation but the specifications of our implementation (2019, On-Prem, Classic UI) have made it difficult to discern the next steps.

It would also be great to automatically generate lists when subsites are created too. Would a similar process be used to accomplish both? Or are they different solutions?

I have access to Sharepoint Designer and Visual Studio. I’m familiar with Sharepoint Designer, it’s purpose, and how it interacts with our Sharepoint environment. Not as familiar with Visual Studio, so I dont know what I dont know about the tool.

Any help in the right direction would be much appreciated. Thank you!