Starting a nonprofit is time-consuming and takes resources, but the benefits of tax-exempt status and legal legitimacy are substantial. The following are two sites that you should become familiar with, along with two links with advice for beginning your nonprofit venture. The Legal Documentation tab, as well, provides links to helpful guides and examples for getting paperwork in order.
Non-profit or For-Profit? Basic Considerations [USA and Canada]
Comprehensive Guide to Starting a Nonprofit
How to Form a 501(c)(3) Nonprofit Corporation
How to Start a Nonprofit Organization
Hurwit & Associates State-by-State Filing Requirements Tool
CMC Toolkit
If you're looking for the tax requirements for your nonprofit, this page on the IRS website is a good place to start. Exemption, unrelated business income, employment taxes, filing requirements, etc.
Nolo.com has provided some free legal and management articles for nonprofits. They are intuitively displayed and clearly written. There are approximately 20 articles.