>how long did it take?

Still working on it. The big decision is whether or not it should be for profit or nonprofit. Economics (funding streams) has a lot to do with it. One of the major challenges for nonprofits is finding funding. After we incorporated, the funding situation was hot for a quick minute (year or so) and then it wasn't. You have to plan for that.

>where did you estb it?

MA even though the board members were from all over the country.

>what are the most challenging parts of starting one?

Engaging a board that is not local, sees each other a couple of times (or less) per year. I didn't submit the completed 501(c)3, yet, because I am trying to decide whether or not to be nonprofit.