I am doing this....on Etsy. There are a lot of people who sell fabric online...so I would do a lot of window shopping on different sites and see what they are charging and can you compete with the prices.
I sell previously owned fabric...buying can be very reasonable if you are in an area that a lot of people live and willing to wait and shop when someone sells their mothers stash. Selling retail means buying in quantity to get the best price. So check that out too.
I know it can be done...hope you get your chance to fulfill you dream.