Hire a lawyer.
Ok, jokes aside, hiring a lawyer may be a good option. Filing for a 501c3 is difficult and comes with a lot of variation depending on the state you are filing in. You don’t only have to deal with the IRS, you have to deal with the Department of Revenue Services in your own state as well as the members of your new board.
If you don’t want to hire a lawyer, there are a lot of resources out there that can help you create a checklist for your state. The issue that I’ve run into is A) it’s not my corporation, so I tend to have to ask my supervisor a lot of questions because she is the director and the only person who can give me the ok signal when needed and B) filling out tax forms can really really suck. They require a lot of information and will time out constantly while you’re searching for stuff.
The bottom line is that either option, hiring a lawyer or doing it yourself, will have pros and cons. The decision will most likely rest on what aspect of your life is currently most valuable: money or time.