Gday Blackman,
Im the SDA here so maybe I can answer some of youre questions.
Arianism came through the Adventist movement and to this day some SDAs are still Arian. When Walter Martin studied Adventism in the 50s he found to his amazement that on official church papers both Arianiam and the Trinity were taught of course the Trinity doctrine is the official one taught by the SDA church.
It should be remembered that to the lead up to the great dissapointement in 1844 the Milleriterites were diverse in their beleifs and they had a wide range of beleifs because tehy came from other churches and were members of different churches while still holding to Millers idears
The SDAs have birthday partys just just like the majority of the people out their.
The SDAs use historicism to interpret last day evens just as the JWs do. In SDA circles there has been a reaction against historicism because of its 19th century connection and the beleife there are just much better interpretations available.The only other church useing the historicist method is the worldwide church of god.
SDAs together with the christadelphians and JWs all beleive in soul sleep but all SDAs [the great crowd ] go to heaven with the 144000 Jehovahs witnesses.