This is a big topic. I'll start with a few general observations I've had over the years.
From what I've seen, most teams start from either a shop/bike-type-company (go to any local group ride), a racer who has contacts (Slipstream is sponsored by a wealthy cycling nut, so was Mapei), or a business looking desperately to sponsor something (7-11 sponsored the team and velodrome since they couldn't build the Olympic pool prior to the 84 Olympics).
Many teams evolve from a core of racers who want to race together and have some contacts who will offer sponsorship.
Do you want a local/shop team? A regional level team (Snow Valley in the US)? A domestic pro team (Navigators in the US)? Or something bigger (Slipstream, Discovery, Mapei)?
Sponsorship - it's like any other selling job - you have to have a compelling reason why a company should sponsor a team. Competitors to those sponsorship dollars include print/radio ads, internet ads/blogs, some mascot guy waving around the company's sign on the street corner, and all the other various people who want sponsors from the same company (cancer/ms/cf/etc fund raiser, local fire/police, charities, artists, local parks, etc). Convince the moneyholder that your team will make them more money than all those other things and you have it made. Or convince them you'll make more friends than they could on their own (perhaps Amgen was approached like this, and you could try tobacco companies, for example).
Since sponsoring cycling at anything but a Discovery level is probably not really that profitable, most sponsors do it for other reasons - tax break, get rid of the pesky guy asking for sponsorship, they love cycling, they're a member of the team, etc.
How do you start a team? In the US you simply pay a club fee. I think it's $125. Then you have to run or help run a race during the year to keep your sponsored status alive (i.e. you can wear team jerseys in a race). Incidentally, holding a race is great publicity for sponsors, it helps the sport, and you get to wear your team jerseys next year. Hard to beat.
What do you need to do to keep a team running? That's not officially documented anywhere in USA Cycling.
hope this helps get your creative ideas flowing,
cdr