Here's how I start bands having started at least five so far, four still in existence.
1. Select a buddy to partner up with. Don't try to do it alone.
2. Select genre. In this case you've selected Big band. But will it be a classic big band or have a mix of funk, blues and swing?
3. Select a practice venue that can house at least 17 musicians.
4. Create a site for communications. My latest incarnation uses Google Groups. (If you want permissions Ed, ping me.) I store music recordings of our songs, setlists, contact roster, and sub list for example.
5. Pick a ringer for each section (sax, bone, trumpet, and rhythm). I usually try to make the whole rhythm section one of semi-pros.
6. Start building library of music. Borrow to try them out and then purchase as necessary. Some music can be borrowed from the Seattle Public library for example. My new WBB has 58 charts to start the first year with. They are all classic swing charts.
7. Send out notice to music aliases, local newspapers, and through networking for musicians. Make them audition unless you've heard them already.
8. Set up a regular practice schedule, usually a minimum of twice a month if you band mates will support that.
9. Do some free gigs at senior citizen venues, local malls and the like to build confidence.
10. Decide how often you want to gig and start building relationships with gig opportunity types: restaurants, malls, coffee houses, and the like.
Not required by recommended is to get BMI and ASCAP membership. I do this through the
Association of Concert Bands for less than $300 a year.
Once you get going you'll want to decide how to do mic'ing and sound. I don't usually use mikes, but most of the big band do. So you'll want a dedicated sound guy if possible.
Okay, what did I forget. Don't make this a democracy; those bands usually fail. Someone buys the music and sets up the band. Listen to the players but don't move on every suggestion or complaint.
Good luck!