Please advice me on checklist filing i-130 for son (above 21)

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I have a GC and I am planning to apply for i-130 for my two sons( both above 21 of age, unmarried and I am their mother). Please let me know if the following documents will suffice,

Check of $535 made payable to Department of Homeland Security 

   --Cover Letter
• G-1145, E-Notification of Application/Petition Acceptance
• Form I-130, Petition for Alien Relative
• Copy of Petitioner’s GC
• Copy of Beneficiary’s Birth Certificate
• Copy of Beneficiary’s Passport (Biographical page)
• Copy of Beneficiary’s Passport (Visa and stamped passport page)


(I understand I need to make separate applications for each of them)

I spoke to an attorney about the filing to clear some doubts. I have some experience with this process as I filed for my GC myself with some help from my daughter. It looks like a straight-forward case to me, but do you guys recommend hiring an attorney?

Also, what's the average waiting time for an i-130 to be approved?

Thanks!