It means he becomes a native Outsider or Outsider (Native) in 3.5.
He becomes immune to spells that specifically target humanoids such as Charm Person, Hold Person, and Dominate Person since you no longer have that type.
You are not considered an extraplanar being on the Prime Material Plane so you cannot be Banished or Dismissed from there.
You also gain darkvision 60' (this is not magical so will function in an anti-magic field).
You do NOT automatically gain DR or elemental resistances unless the Fatespinner description says you do (IDHMBIFOM).
I played an Alienist from T&B who also achieved Transcedence at 10th level, becoming an Outsider. With the Alienist, specific physical changes as well as bonuses to Intimidate are cited. I'm not sure what is the case with the Fatespinner. If it doesn't say specifically, then you'll have to role-play it.
BTW, it specifies in 3.5 that Outsiders do NOT need to eat or sleep, though they must breathe.
Also, are there different outsider templates to apply to my character, or is there just one that does what is stated above.