My Team did this some years ago. It is really nice to have the financials separated from the school. Unfortunately this is not a do it yourself kind of thing. You need to find an accountant or somebody familiar with the process to guide you through it. You need to create a corporation with bylaws that fit the criteria. Then there is the IRS filing (by sure not to have patriot or tea party in the team name) Once you have the 501C status, it requires regular filings to maintain it. Your also have to track your money in such a way that if you are audited, you can justify your expenditures. All this really is not that hard compared to building a robot in 6 weeks, but is needs to be done correctly. The IRS is a lot worse than the GDC & they do lawyer their rules.
So the best first step is to find a Mentor with the background to this. Parents, sponsors, PTA, the local Rotary club are some places to look for this person.