Problem: Historically we built Site Templates and WSP to build up of SharePoint solutions. With the current state of SharePoint it's not advisable to release Full Trust Code (FTC).
Initial Hypothesis: So I often tend to write CSOM for custom provisioning and asset deployment. I utilise the Tenant Admin API for provisioning site collections and then CSOM SharePoint in C# to provision and deploy my assets.
PnP has a great library to provision assets to base you solution on, customising and building XMLfiles allows you to quickly build repeatable SharePoint solutions that are easily configurable.
Also InstantQuick has a solution called IQApp that is worth a look at.