For more info see these:

[url=http://www.bolterandchainsword.com/index.php?autocom=ineo&showarticle=456]Black Templars: A Comprehensive History[/url]

[url=http://www.bolterandchainsword.com/index.php?autocom=ineo&showarticle=455]Imperial Fists: A Comprehensive History[/url]

The information about Sigismund is not all in one place, but there's tons of information in both articles relating to the Horus Heresy, the role Sigismund and the Imperial Fists played as well as almost all you can find about the Black Templars and Emperor's Champions in general.