When should I start gardening for this spring?

Sounds like an ambitious and fun project! To start, look up the date of the last freeze for your area and go from there. Some plants need a 6-8 week head start prior to that date if you are planting from seed. Other seeds have to have the ground temp warm enough to germinate. So, when you plant, really depends on what you plant. You will also need to check with the farmers market in your area to see what the guidelines are for becoming a vendor. Good luck with everything! Keep us posted on how it goes!