1) you can submit application paperwork 6-months prior to the 5-year mark.
2) I did this on my own. It’s quite straightforward and there are tons of great resources online.
Two things to help you:
1) use Adobe Acrobat Reader to fill the form. The forms were created with Adobe’s tools (or so it seems), so validation is built/in. Also, there are sections where the response to the first question dictates the next few responses; with Reader, if you don’t check the box, you don’t need to fill N/A in the rest of the fields for that section. This might seem like a small detail but when dealing with USCIS, you don’t want to take any chances. With the right tool, you don’t have to worry.
2) if you don’t hear back on your application post the interview stage, request an appointment with the reason that you want to provide additional details or answer follow-up questions. My application got “lost” in a pile somewhere and took 75-days to make it through to the step wherein I could schedule an oath ceremony. The wait is nerve-wracking, to say the least.
Good luck and send me a message if you need any help. Once again, not a lawyer; just another immigrant who went through naturalization (and now filing of my dad’s GC) on his own.
You can submit the application 90 days before your 5th year anniversary as a permanent resident and unless you have an issue - extended time outside the US while a permanent resident or a criminal record - it's a really easy application that doesn't require the assistance of an attorney.
Is it advisable to file for citizenship on your own?