The next place I'd look is actually Westin Phipps arc for a combined story, touching on what happens with Banes and Fortunatas. We don't have a lot of info on the Tarantulas, other than the process can be fatal - I get the feeling from a few references (of being "envenomed," among other things) that it doesn't have a *high* success rate.
Widows, as far as I can figure, are psychically-sensitive children (usually female) that Arachnos takes and indoctrinates at a young age, nurturing their psychic potential. The ones that show only moderate amounts of psychic ability usually end up becoming Night Widows (assassins and saboteurs), while the ones with great psychic ability end up becoming Fortunatas (who are aiding Lord Recluse in trying to see into the future).
I've looked on Paragonwiki and couldn't find much info there other than Ghost Widow is in charge of the Widows, Fortunatas, Tarantula Mistresses. Is there someplace someone can point me to to find out background info on the Widow Corp (if that's even what they are called)?
I'm working on an Arc and need more info to flesh out a story.