Big Island lawmakers are considering a bill that would formally allow farmers to give tours and sell souvenirs on their property. The Hawaii County Council will hear arguments Thursday on splitting agricultural activities into major and minor operations. The bill would limit minor operations to 5,000 visitors annually and a maximum 100 visitors per week. A major operation would be allowed up to 30,000 visitors per year.   Opponents worry the measure will pull farmers away from their primary occupation of food production.