When creating a Helix based solution with SXA is it ok to just use the Feature and Foundation layer templates as-is for our content items, or should we be creating derived templates in our Project layer? If we should be doing the latter, is there any automated way to do this?
When you are creating new Tenant and Site in SXA we have it automated with our scaffolding logic, you will find actions to create tenants and sites and they basically do all the work for you. You don't need to think about defining any inheritance as those scripts will do this for you (unless you have any custom extensions).
When you are creating tenant then inside of
Template/Project/YOUR_TENANT_NAME path needed templates will be created for you. Take a look here:
As you can see everything is there. Of course you can extend it by adding your base templates but you should inherit from SXA page. We are checking this in code and if it won't be using our base template then your page might not be recognized as an SXA page.