Custom Manager Pages: How to link and retrieve post variables?

I'm building a menu for the user to view, add, delete and edit products. I'm using Custom Manager Pages and custom tables inside the Modx data base.

I'm successfully listing products, but I need to add products with a form.
The form within the cmp should redirect to a php script, which only inserts the product into the database, and then links back to the cmp that lists the products.

Since the cmp is inside the Modx manager, I don't know how to set the path for the php script and then to return to the cmp. The php script should retrieve the post variables, as well.

I still have to resolve how to edit and delete products, but I guess that it will be similar to this problem.

Thanks in advance for your help!!

Details:
Modx Revolution 2.5.7

Did you try MIGXdb? With this, it is easy to build your CMP.
Or are you trying to go the hard way?