Welcome to the forum. Yes there are hacks here on MobileRead. I'll check where and edit this post with a link later. The best ones IMO are the clock and the delete ebook. Also check out bookDesigner & Calibre softwares that you can use to reformat ebooks (if they do not have DRM) for use on the PRS-500. You can find them on the MR WIKI or see links below.
One thing you should know, if you let the 500 discharge completely you will need to use the AC/DC charger since the USB won't charge it if it is completely dead. If the battery isn't completely dead you can recharge from your computer via USB.
You should be able to register it with Sony and purchase books from them or you can also find appropriately formatted books at
Baen or
Fictionwise's multiformat & probably other places too.
Good luck.
BookDesigner
Calibre