Where would I suggest people learning about Haides start? I would have people start with the ancient writers, but NOT end there. There are several Hellenic Polytheist websites with information and also a couple of websites with a good deal of general information.
I would particularly recommend Theoi.com as a good one because the site owner cites original sources and has the page set up so that there is also a library of ancient texts in translation. I personally like the Athannasakis translations of the Homeric and Orphic Hymns honoring the Theoi better than the Taylor translations, but this is personal preference.
Neos Alexandria is one of two organizations for Hellenic Polytheists that I would recommend. Although they do not have a devotional for Haides in their publications, they DO have many devotionals about the other Hellenic Theoi as well as several ones for the Egyptian deities.
There is also Hellenion which has information on the Theoi on their website as well as an annual calendar that includes the Attic festival calendar. Hellenion has a forum and Yahoo Groups where questions can be asked which will usually be answered fairly quickly.