Great Grandfather Severin Ludvigson origins?

Hello, Today is a pretty terrific day. A riddle lasting three generations has been partially solved. The riddle which is now partially solved is that I now know the real name of my Great Grandfather and his parents all from Norway. My Great Grandfather Severin Ludvigson was born in 1879 and imigrated to Michigan USA as a young child sometime between 1882 and 1884. The ole family history only partially matches up with the following information provided by the State of Michigan. According to the state of Michigan, Severin Ludvigson (born 1879) and his sibling Mareusius Ludvigson (born about 1875) were abandoned by their father in Menominee County Michigan and made dependents of the county probate court and committed to the State School in Coldwater Michigan in August of 1884. The State of Michigan records indicate their mother was an inmate of a "Lunatic Asylum" in Norway. The fathers name is listed as Ludwig Matherson. The mothers name is listed as Marin matherson. Severin was indentured to the Graham family in Hope Michigan from 1887 until 1898. While he was never apparently adopted by the Graham family he appears to have taken their name in as much as he was always known as Severin Graham. The riddle which is now partially solved is I now know what Severin's original name was, and the name of his mother and father. Of course there is a great deal to discover which is why I have thrown myslef into this message looking for assistance. Can someone please steer me in the right direction in what I should do now? I would like to discover what ship Severin Ludvigson, his brother, and his father Ludwig Matherson made passage on. I would like to know how I might best find out more about the parents, and where they may have originated. Is there an Idiot's guide to searching for Norwegion relatives somewhere on the web. The entire sirname is a bit different from my english german roots. I have not had a chance to pour over this site, and I hope to do so, I just wanted to start my jorney with relaying my excitment of my Norwegion roots, and my desire to dig deeper. Best regards, tree aka Eric