Do you want to start a race team or a club type team?
There are liability issues involved in leading rides, promoting races, etc. so beware of those. If you are doing a race team, you can use US Cycling or NORBA insurance, but you have to be officially members of either USA Cycling or NORBA and then you need to sign up for their insurance, etc.
As far as getting sponsors, that can be the easy or hard part. Usually, a sponsor will donate a certain amount of money to put their name on a jersey. Remember jerseys and kits are rather expensive, most companies that make them have minimums, so you have to order a certain amount, to get prices. If you don't they are really expensive.
Anyway, there are a lot of things involved in starting a team and I can't list them all here, but be careful with liability issues, you don't want to put yourself personally or your home or assets at risk.