We are currently working on the MVP for our startup. We do hope eventually to include premium features specifically for business and content producers, but our MVP will be a consumer-focused free service.
There are many strong articles detailing how we should find ten people who will say that they'll buy the product. (Good example: http://blog.asmartbear.com/customer-validation.html) Does anyone have advice on how many beta sign-ups could serve as a reasonable gauge in lieu of customer validation?
If you must use beta users as a metric, be very conservative and realize that most of those signed up will probably not even use the beta, let alone buy the product (this varies by industry and product of course, among many other factors). In your case, you might think 1 in 100 signups will become customers, or 1 in 1000, or 1 in 10. Since we don't know what the product/market/marketing methods etc are, you're the best one to make the guess.
But yeah, you should talk to real potential customers.