I am retired and travel a great deal. I would like to offer my services to house sit (take care of plants, pets, etc.) when I am home to suppliment my sagging IRA income. I would like to either get bonded or purchase an umbrella insurance policy to protect myself if an accident should occur. I am personally worth about $500,000 right now, including my home. What amount should I insure for, what are approximate costs, and how do I go about it?

Call your insurance agent that handles your home and car insurance, Most offer various forms.
Umbrella insurance normally starts at about 1 million and will pay after your other policies stop, and require often 300,000 liability on your standard polciies.