Hi.
If I understand you correct, then the guide line for customizing your own elements will help you:
http://guides.alchemy-cms.com/create_elements.html
Same with the page layouts:
http://guides.alchemy-cms.com/create_page_layouts.html
Default values can be added via the default key from the elements content description. I.e.:
- name: my_custom_element
contents:
- name: content_name_1
type: EssenceText
default: Lorem ipsum
To remove/hide default elements, just delete them from you config/alchemy/elements.yml file.
I hope this helps.
Let us know if you need more information.