What's the best way to start idea extraction with a large email list?

Hello Indie Hackers,

I am a developer who also manages an email list of 300,000 + subscribers for my client. We are in the early stages of idea extraction and would like any tips or insight on the best way to go about doing this.

I'm planning on sending a short survey to the list asking for pain points, repetitive tasks, etc. Then, following up for phone calls for those who respond.

My question is, at what point do we need to pick an idea and start sketching it out, or building the MVP? I don't want to overthink this step but also want to make sure the idea is a solution that will be used.

Any feedback or strategies for ideas extraction would be greatly appreciated.

Thank you!