Redmine

I'm creating an interface that auto creates projects and tasks for specific orders. Essentially an order management system. A few things that would be nice to be able to set in the API:

Be able to create a sub project inside another project.
Be able to create milestones for a project.
Be able to edit and set custom fields
Be able to edit/create task relationships

Looking at the code examples I didn't see how to do those things, please correct me if I'm wrong.