epidemiology discussion

The mayor of your city wants to allocate funds to open several  curbside healthy food markets/ farmers markets based on the hypothesis  that people who utilize curbside healthy food markets/farmers markets  regularly (defined as once a week) for their groceries have healthier  weight and are likely to control of their weight as compared to people  who do not utilize them regularly.

As an epidemiologist you request and succeeded in getting a small  amount of funds to conduct an epidemiological study to test the above  hypothesis. How would you design this study? What are some of the  potential confounders and or biases that can influence the results of  study? How can you minimize them and report the results objectively?