re: "is there a template for requirements document?"
No.
As a freelancer who works on projects such as you are describing, here is what I do NOT want to see:
A fixed-price job posting with a long list of requirements, a wall of text. I will just move on and look for a project that won't waste my time.
This is what I DO want to see: an hourly contract with a paragraph or two describing your concept generally.
I am only speaking for myself, of course.
You are the client.
I recommend that you post an hourly job, describing what you want.
Then hire three to five freelancers.
Then pay them to create the requirements document.
There may be one person who is the primary writer of the document, doing so based on input from you and the other team members.
You will tell them what you want in the project, by scheduling Zoom meetings or communicating via group chat such as using the Upwork Messages tool or Slack or email or Skype.
Honestly, you should be able to create the requirements document within a single hour-long Zoom meeting.
You can use a shared document, which as using Google Docs.
Don't let them make the requirements document too detailed! It just needs to have enough detail that lets you figure out what modules and general functionality there will be in the project, and lets you assign tasks to team members.
Assigning the team members tasks and having them complete the actual work is more important than having every detail written down in a requirements document. You are not building a skyscraper. You are building something digital. You can have them change things.
Let them write the requirements document. Then assign tasks to members of the team until the project is done.
As the team works on the project, you can check off what tasks have been done. You can keep track of who has been assigned what tasks. You can add new tasks.
You can do this within a spreadsheet, or a text document, or a dedicated tool. But keep it simple. The required document is not the end goal. It is a tool to help you achieve your goal.
While you work with the team, look for the ones who are not productive or who turn in low-quality work or who are too expensive. Close their contracts. Continue working only with the freelancers on your team who provide you with the most value.
