Is it possible to choose as a creature type Elemental for Unclaimed Territory and use it to turn Stirring Wildwood into an Elemental 3/4 creature using said Unclaimed Territory?
Yes, you can choose Elemental as a creature type; no it will not do anything here. Activating the ability of the Wildwood is not casting a creature spell and it is not even an Elemental when you are activating it. You can obviously use the Territory to produce colorless mana but you cannot use it for the green or white mana requirement for the land.
Unclaimed Territory
Stirring Wildwood
Yes, you can choose Elemental as a creature type; no it will not do anything here. Activating the ability of the Wildwood is not casting a creature spell and it is not even an Elemental when you are activating it. You can obviously use the Territory to produce colorless mana but you cannot use it for the green or white mana requirement for the land.