Danios are fast bullet type fish. I wouldn't keep them in a 10 gallon, personally, because I don't think it gives them enough room to swim fast.
A school of cories is a great idea, get at least 3, 4-5 would be better. If you go with a dwarf gourami only get one.....a ten gallon is small for that fish as well but one would probably be okay. I would stay away from the neons cause they aren't always that hardy and seem to sometimes die off easy forcing you to constantly replace them to keep up a good school. A betta usually does great with cories.....but every once in awhile you get one so mean it can't live with anything. And a betta will also limit fish choices in the future.
I would definitely get the corys and maybe a school of some hardier tetras. Definitely avoid tiger barbs & sharks. If you see something you like but aren't sure about look it up in a book. The fish stores usually sell fish identification books and you don't have to buy one(though it would be a wise investment) you can just use it to check on a fish you are unsure about. This is generally more reliable then just trusting an employee you don't know.