I'm a sheep.
A lovely, fluffy sheep.
Does the creature's normal casting cost have to be paid?
Does the 2 mana have to be spent?
Yes. Spawnpoints, like familiars, pay with their own mana first, and then use the mage's mana for what still needs to be paid.
Is this in addition to the normal spell it can cast for being a spawnpoint?
The spawnpoint trait gives an object the capability to cast spells during the deployment phase. The individual object's text is then used to specify what kind of spells it can cast (in this case - holy creatures) and any restrictions (in this case - the requirement to have 2 mana). Without the individual text, the Temple would be a spawnpoint unable to cast anything.