MTG Salvation

I was in a situation wherein I had 3 mana, and wanted to play Goblin Freerunner for its surge cost.

If I play Expedite, and then immediately play Goblin Freerunner for 2 mana, Would the creature be on the stack above the instant, and therefore be on the field when Expedite resolves? If so, would I then be able to select Goblin Freerunner as the target for Expedite?

Or would I need to choose a valid target for the instant before I can play the creature?

You wouldn't be able to cast Goblin Freerunner (or any creature) before the instant would resolve anyways, not unless it has flash. And even then, you would need a valid target when casting Expedite, and the Goblin would not be one.

The Goblin Freerunner would need to be on the battlefield before casting the expedite the target of a spell is declared while the spell is being cast, not when it resolves.