no its not ok, that is too small of a tank for pretty much anything. Maybe you could put 2 male guppies together or 2 females together but I'd recommend 2 females.
Fisht... you should know better than that.. sharks get much much too large for a 1 gallon tank!!!!!
i would stick with 1-2 male guppies, they are very bright and colorful, the females are much more dull and are usually pregnant when you buy them. but dont mix the genders together, they breed like crazy and you will end up with way too many.