Carts are typically restricted to certain areas and to certain hours. Permits are usually required, but the fee is nominal. You can select those features that would be good for your community, and then work with your planners and elected officials to create the desired policies. But the city almost never provides technical assistance, carts, business training or other business support services to the vendors. Vendors are specialty retailers, selling a specific type of product like toys or hats or dried flowers.
Some vendors make what they sell.
A craft person may sell their entire annual production in a mall during December. Some vendors sell stuff that is made by another person. You might have one group of people making stuff and another group selling it. The vendors could be strictly on a commission or on a salary, but usually they are self-employed. You could help recruit and manage the vendors as a partnership with a mall or business association Or, you could have a special section in a downtown store or in some public place.