Http Performance - Many small requests or one big one

Question

Scenario:

1. In my site I display books.
2. The user can add every book to a \"Read Later\" list.

Behavior:

Answer 1

Option 1 sounds good but has a big problem in terms of scalability.

Option 2 mitigates this scalability problem and we can improve its design:

Client side, via javascript, collect only displayed book ids and query once, via ajax, for an array of read-later info, only for those 30 books. This way you still serve the page fast and request a small set of additional info, once with a single http request.

Server side you can further improve caching an in memory array of read-later ids for each user.