Unitarianism is a belief that diminishes Christ to a lesser being, among other things. Seventh-day Adventists do not believe in Unitarianism. Seventh-day Adventists believe in a Godhead consisting of three equal Persons, who are one in nature, character and purpose {PP 34.1}
When Christ came to this earth, he voluntarily assumed the nature of man, which also included humankind's vulnerability to temptation and falling into sin. Learn more by clicking on the link.
Yes! As Paul stated, "1 Corinthians 5:7 "Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:" (Read more on this important subject by clicking on this link.)