Complex sentence: First came the St. Jerome's Summer Series each Sunday afternoon featuring' new' bands of the time like The Presets and Architecture In Helsinki; next it extended to include a monthly Saturday night called Brains (which was actually a residency for The Avalanches).
Split into simpler sentences: First came the "St. Jerome's Summer Series" each Sunday afternoon, featuring "new" bands of the time, including The Presets and Architecture In Helsinki. They then included a monthly Saturday night called "Brains" (which was actually a residency for musical act The Avalanches).