Creating a Voiceover project does not deduct any quota. Once you've created your project, quota will be deducted every time material is generated. Similar to Speech Synthesis, quota costs for voiceover clips are based on the length of the text prompt. SFX clips will deduct 100 quota per generation.
If you choose to Dub (translate) your Voiceover project into different languages, this will also cost additional quota depending on how much material needs to be generated.