Hi,
This project looks very interesting for me. The answer for your questions:
1. It can’t be closed, because everyone has the form link can access it.
2. You will share the link to the people you want via email or just copy the link and share it. All users will use same link.
3. You will setup the form to collect the email ID of the user, so by all means he should sign in before submitting the form.
4. Yes, it will provide.
Timeline will be 3 days from awarding the project. I will provide you full support until all your requirements are met. Hopefully I covered everything you need to know. Feel free to contact me if required anything else.
Best regards,
Abbas