If you are friends with this person on Facebook you can go into your Page Settings and edit Page Roles. Assign them the role you wish, depending on what you want them to be able to do. They will then have access to the Page. In your case I would assume you would assign whoever as an Editor. If you're on your desktop and doing this, Facebook will give you a layout of who can do what in different Page Roles -- you will see link at top of page when you hit Page Roles under Settings.

Regarding the delegation and automation part of your question. It is possible for you to use a scheduler like Smarterqueue or Hootsuite, which ever suits your need, then get your FB Virtual assistant to upload all your articles, and posts etc (I use Smarterqueue!).

You assistant can also determine what articles, and posts did well and which didn’t, and amend accordingly, from the scheduler stats.

This would take care of the automation part, but wouldn’t you still want to engage with the people that respond to your posts? Particularly if you’re trying to build up a following, to sell your book and get clients. Maybe consider developing a social media strategy, if you haven't already, so you and you virtual assistant know what the aim is, otherwise you may end up just wasted your time, energy and money.