JOEL - I really don't know much more about James Strang's claims than what the Strangite website says about it. I answered a similar question at this page, using information from that website
Considering what happened to Strang and with most of the members leaving his church, in my opinion it is quite obvious that his organization was never sanctioned by God. As the scriptures say about prophets, "By their fruits ye shall know them" (Matt 7:20)

Personally I believe that the plates that were found were forgeries, manufactured by Strang in an attempt to provide credibility for himself as a prophet like Joseph Smith, who of course also translated plates.
In regards to how Brigham Young became president, since there was at the time no precedent and no clear procedure providing for succession to the office of president, after Joseph Smith died competing views arose. In accordance to D&C 107, Brigham Young, then President of the Quorum of the Twelve Apostles, presented the proposition that the Twelve, ordained apostles who held all the keys necessary to govern the Church, should be sustained as the authorized leaders in the absence of Joseph Smith.
After several private meetings during which leaders reviewed the options, on August 8, 1844, thousands of Church members gathered in the grove near the Nauvoo Temple to decide by a public sustaining vote whether Sidney Rigdon, who was the First Counselor to Joseph Smith, or the Twelve would lead the Church. Sydney Rigdon took the stand first and spoke at length of his right and position as First Counselor. Then Brigham Young presented the view on how the Twelve should lead as a group. The result was overwhelming support recognizing the Quorum of the Twelve Apostles as the authorized leaders of the Church, specifically with the keys to act as the First Presidency and with the power to reorganize the First Presidency. Although that decision was clearly sanctioned by the 1835 revelation and was in harmony with the position of the Twelve in Nauvoo, many Latter-day Saints claimed a further deciding factor: when Brigham Young spoke on that day, his voice and appearance bore a striking resemblance to those of Joseph Smith. Wilford Woodruff, one who was present, later said that if "I had not seen him with my own eyes, there is no one that could have convinced me that it was not Joseph Smith" (Deseret News, Mar. 15, 1892)(information taken from "The Encyclopedia of Mormonism").
So the selection of president was made according to instructions from God revealed in existing scripture and the common consent of the members, who all received their own personal revelation that the correct choice was made. Several members who did not agree with the decision went off with various other leaders, including Sidney Rigdon, William Smith, Warren Parrish, and James Strang. In all about 130 different groups split off from the main Church after the prophet's death, with very few of them lasting more than a few years.