Common goldfish have shorter fins and comets have long fins. that's pretty much the difference between the two, as both are slim bodied shape and fast swimmers.
Goldfish will eat just about everything. They would enjoy the bloodworms and if you want to try the recipe on this site go ahead. I think most of us feed frozen peas popped out of their skin and bits of orange as a treat.
Goldfish treat most live aquatic plants like we treat potato chips...
The love to munch on them! Make sure you place only aquatic plants that your pet shop approves as safe for aquariums since some common regular house plants may be poisoness.
Good luck with your new little friend!