Are you ready to work on brand building for several years? Do you have money to do online/offline advertising? Do you have motivation to keep the site fresh and up-to-date with new unique content even when traffic from Google is mediocre? Can you fight off temptation of getting unnatural backlinks when all your competitors are buying links and dominating page 1 results and getting away with it because they are big brands?
It can be very frustrating . Is the niche you choose something you really like/love personally? One Google update and loss of traffic can kill your motivation if you're in it just for the cash.