1) This one is up for grabs.
2) There are several spellings, based upon source.
3) Take your pick!
4) Examples
"Tinker Bell":
. . . Disney video tape credits
. . . Disney Archives description of Peter Pan movie
. . . Name of "Treasures" shop in Castle
"Tinkerbell":
. . . Cathy Rigby Peter Pan Musical credit
. . . Disney.Com details of tink's flight
. . .
Disney Cruise Line on-board activities listing
. . . Several costumes sold by Disney
. . . Disney.Com description of Peter Pan Flight attraction at WDW
. . . The Movie "Hook" credits
"Tinkerbell" AND "Tinker Bell":
. . . J.M. Barrie stories spelled it both ways