Small random-orbit or pad sanders make this job go faster. (Wallis first covers these boundaries with Synkoloid patching compound so no edge is visible after sanding.) As shown, you want to make sure that there is a feathered, smooth transition from exposed wood to old paint. For areas that might get close scrutiny, you can follow up with a 100- or 120-grit rubdown to erase any scratches.
It's okay to receive ballpark figures over the phone however, insist upon an in-home estimate. A quality painter will help point out why certain parts of the project might be more expensive and can even talk through the repair process if it's necessary. A painter should also ask questions regarding access to the painting site, where they should park and if any HOA rules prohibit hours of work. House Painting