Is it better to send audio questions than just text?

You're right, it's better if you send your questions as audio (with text) so the guest can hear your voice.

You're right, it's better if you send your questions as audio (with text) so the guest can hear your voice. You can always replace this audio later by re-recording the questions, or adding a narrative storytelling.

You can create templates in Rumble Studio that include the audio, so you can easily duplicate the template to reuse the audio questions in different interviews. 

Of course, the simplest way to scale your podcasting is to invite multiple guests to the same interview.