Oh you have found the first big step...
This is just me talking... If you are using an online source, please do not sign anything at all. Matter of fact if you have already given them your SSI number and not signed anything yet go online to the Social Security Department, make sure you have your account set up and you are password protected now!
I almost got scammed from a big online add saying they can help me get through the filing process. Before I signed, I found out they had logged into my Social Security account, set it up with another email and address. I was able to stop them dead by placing an instant request to block my account until *I* was able to verify who I was and that I was the actual owner of my SSN. Do not become a victim twice.
I recommend if you want legal assistance, find someone local, someone that handles SSID claim assistance, and someone you can talk to face to face. I did that, they gave me some very good ideas on how to proceed and what will be needed from me. They laid out the path and I just followed it and did all the work. Just over 2 months later I had a check and so did they. I think they got 25% of my first check. SSID paid my lawyer directly. I had money in my bank account 2 weeks before SSI notified me that I had been accepted.
What SSID is looking for this year now that they acknowledge Fibromyalgia? A medical history going back several years with a diagnosis of FMS from a Doctor. Inability to have worked for at least 6 months. If you have that, I might just go through the seemingly large amount of online paperwork. Do NOT look at the whole pile, just start one section at a time. It would help if you have a copy of your medical and employment records in hand when you start filling the forms out. Just take it one step at a time. You can always stop and restart where you left off. Submit it when you are ready.
If you believe that SSID may try to fight you, and or your situation is urgent, I would recommend that you have a good Law Firm behind you. I believe that SSID sees that and it may help your position against SSID challenging you in court and loosing anyway.
Again, this is just me talking like I would talk to any of my friends... I am by far no Lawyer, but I am now paranoid against ANY online assistance mill out there who may take advantage of our illness for their gain at our own efforts.