As part of the Developer Program, you will be able to request access to a personal developer sandbox that will be fully tooled to include Innovation Suite, APIs, and a library of reusable components. Developing in a personal sandbox gives you your own flexible development environment where you can get comfortable with the Innovation Suite and its features.
Yes, you still need to sign-up for the program to ensure you benefit from the exclusive Developer content and the Personal Sandbox that will be available only as part of the program.
No, that is not a pre-requisite to sign-up for the program.
The personal sandbox you get is only a Development Environment. This does not have a Production Environment with a run-time available to deploy applications in the cloud at this time.
You have unlimited access to the sandbox as long as you use it. The sandboxes will be reclaimed by BMC if there is a week's worth of inactivity. You will have to request a new sandbox once your sandbox has been reclaimed.