Hi Jen – I just realised you also sent us an email about this the other day, right? Sorry for not getting to this sooner. You can expect a reply today 
Company licenses are "floating" and can be transferred between employees. If your company holds 5 licenses, this means that 5 developers can use Prodigy at the same time. One person on your team should be in charge of the license keys and they should always keep a list of the persons who are currently holding the licenses.
Annotators who will only have access to Prodigy via the web application don't require a license.
This depends on your workflow and requirements. The only restriction is that Prodigy can't be publicly acessible and needs to be hosted on an internal network, or behind a password-protected URL. Prodigy is a Python library that starts a web server, so you can also integrate it into your existing infrastructure and stack. During the development phase, we've also found Ngrok very useful – it lets you share a local web server behind a protected, public URL without having to upload any of your data to a server. Some users have also shared their custom setup for managing multiple annotator – see this thread for a cool example.