Strategy for scheduling interviews with users but not TOO many

I want to use our signup queue (and various part of it) to conduct user interviews but not scheduling TOO many.

I'd like to interview people from various profiles. Like whether they're on Windows or Linux or they've been using the product for 1-2 weeks, or 6 months, etc.

I guess I could write code to do this but it's a 1-2 day task and I'd rather focus on other things, to be honest.

I guess one / easy strategy is to send 5 emails, then see what % signup... then just try to figure out how many emails I need to send (on average) to get N user interviews per week.

I'm trying to target 5 user interviews per week.

Apparently YC's recent batch showed that 5 was ideal.