Jekyll Admin related options can be specified in _config.yml under a key called jekyll_admin.

Config Options

For hiding unwanted links on the sidebar.

The following keys under hidden_links can be used in order to hide default links:

jekyll_admin:
  hidden_links:
    - posts
    - pages
    - staticfiles
    - datafiles
    - configuration

homepage

Web page set as the default or start-up page for Jekyll Admin.

Valid values for homepage: pages (default), posts, <collection_name>, datafiles, staticfiles ,drafts and configuration

jekyll_admin:
  homepage: "posts"