1. There's a nice book introducing to Elgg 1.8 in general and introducing to Elgg coding by Cash Costello (core Elgg developer): http://www.amazon.de/Elgg-Social-Networking-Cash-Costello/dp/1849511306/ref=sr_1_2?ie=UTF8&qid=1341344951&sr=8-2

2. I'm not using the bundled zaudio plugn myself, but doesn't it work to play-back mp3s uploaded to the file section of your site when logged out when the access to these mp3 files is "public"?

Like iionly, you could extend the files to plugin to set any file uploaded to be public and use this plugin:

http://community.elgg.org/pg/plugins/project/868269/developer/ripcord/veeplay

It has a nice mp3 player, try it.

Rodolfo Hernandez

Arvixe/Elgg Community Liaison