we use an insurance broker as well. since we also do Christmas lights, our rates are higher as we go on roofs, etc. since landscape lighting can also bring you off the ground doing gutter mounts and moonlighting, you should ask to be covered for some heights, as most injuries and property damage will occur when you fall. the risk of fire from landscape lighting is extrememly small and pretty inexpensive to insure. you will be "rated" at a percentage of payroll and pay that rate at a payroll base of around 10k minimum and it will go up from there.
workmans comp is the same way, it is required in most states, and you will pay a percentage of payroll, our minimum workman's comp policy here costs around 3k per year and covers for us up to 30-40k of payroll and goes up from there.
we also carry "professional" insurance to cover us even if we do something wrong and cause property damage.
we do auto through state farm.