Services are almost always structured as subscriptions. In your case, there's a big question of whether you should use a flat price or charge as a multiple of the products that are being updated with your service.

Unfortunately pricing is really challenging and complicated, and the only way to get it right is to survey and A/B test.

One thing you need to know is this: what's the average number of products a developer creates? If the answer is 1.5, then you wouldn't want to do a "first product updates free" model. But if the answer is 5+, then you have nothing to lose by letting them test out your service with one product before adding the rest. (But then they could also be really shady and use multiple email addresses, so you'd have to verify identity somehow.)

If you're surveying users, you should also ask what they'd be willing to pay. There are probably best practices for how to ask that question, and I don't feel qualified to tell you what I think.