Most Efficient Way of Doing Custom Post Type (book reviews) Search?

I’m making a custom theme for a book review blog. I have a custom post type for the book reviews, so I want to give users the capability of filtering through those (we have about 500) with various fields.

My biggest issue is sorting reviews by Author Name. We want users to be able to sort by both first and last name, so I made custom fields for first and last. My whole setup is like so:

author_first_name – Custom Field
author_last_name – Custom Field
series – Taxonomy
genre – Taxonomy
publisher – Taxonomy
publish-date – Custom Field

My problem with this is that:

1. Some books have 2+ authors
2. We’d like each author to have their own ‘archive’
3. I want to count how many reviews each author has

The above makes me think that maybe I’d be better off using a Taxonomy for the author, but then how could I do that and still make the reviews filterable by last name?

I’d be super grateful for any advice/brainstorming!