For us, the most time-consuming part was the creation of bylaws.
These will define how your group operates. Once these are set, a lot of other 'things' fall into place.
You can use 'canned' bylaws, which someone else can get you, but once I started looking into it, it became clear that we needed rules that fit the character of our group, so we basically started from scratch, taking what we liked from some samples and authoring the rest.
There are a few IRS requirements in the bylaws, but a lot of it is pretty much wide-open.
Get the Start-Up Kit. I actually waited to finalize our appplication until it was published. It makes the form easy to fill. (The attachments, etc. that will be required are still very time-consuming and a little difficult.)
I realize that you have 'a guy' who will do your filings for a fee, but I think you should consider doing it yourself. With you and your leaders 'founding' your organization, you will all be experts in how you are supposed to operate. You will each know the intent behind the bylaws, and you will all have agreed to them.
I think ours cost $750 total, including the filing of an amendment to our Articles of Incorporation that would have been avoided if the Start-Up Kit had been ready 6 months earlier.
But like I said, part of that cost can be attributed to 'Leadership Education'.