I pretty much do as cole does only I dont use any ferts unless the plants are getting big and then I use TTF or fish emulsion/kelp. I sell all my veg starts at $3 each or 5 for $10. you can see all my prices here
https://nodinesplants.wixsite.com/nodinesplants
It is hard to lose money selling plants. If you can find a plug grower near you it makes it really quick to make a fair amount of $. Dwarf flowers of any sort typically sell well especially Profusion Double Mix zinnias. I'd also call Ball and find your nearest rep. He will know all the growers and plug producers and can likely help you more than anyone here. Hanging baskets are also something to consider. Ask other nursery owners around you what their best/easiest flower is for making $ Good Luck!