At Level Level we created an Open Source plugin ‘Clarkson Core’: a Twig based template engine with under the hood a collection of Object-oriented WordPress classes and some lightweight handy features. This, in combination with a basic modern starter-theme and some agreed upon guidelines, contributes to a workflow that keeps comprehensive projects aligned with your high technical goals. Meanwhile keeping the WordPress way of development in mind.
So where do I start?
When you have never worked with a template engine like Twig then start at the begining of Clarkson Core. If you do have some experience with Twig then go on and read our Documentation of Clarkson Core or our Introduction Guide.