Fish food? Just wondering...?

tropical fish food just has more nutrients&minerals because tropical fish are more often more colorful and the extra ingredients in the food helps to maintain a more colorful,healthy and generally much better looking tropical fish as far as cold water fish go they will be absolutely 100% fine eating the tropical food they even end up looking better anyway that's what iv found

You can give them all the same kind of food. It doesn't hurt them. If they didn't like it they wouldn't eat it. Look at it this way: if they were all in the same tank and you were feeding them different kinds of food, they'd all eat each others anyway, but of course you wouldn't put cold and warm water fish together, just an example.

Also, if you have different sexes of the molly, guppy and platys, be prepared to have an overwhelming population explosion. You'll need more tanks than what you have, and it will never stop until you completely separate the males and females into diff tanks, including the fry as soon as you sex them or they'll be breeding as well in a couple of months.

I wouldn't. Fish food is formulated with a specific fish in mind.

Honestly I wouldn't feed the fantails flakes at all. It is better to feed them a sinking goldfish pellet. They would also enjoy blood worms, lettuce, peas, orange slices, or zucchini slices.

If you don't already, remember to buy algae wafers for the pleco as well.