is there a right order for adding fish to a tank

I had heard to start with the small fish to cycle your tank, then to add the bigger fish later. But the lady at petco, said that you can't add bigger fish because then the ones that are already there will try and establish dominance. So what do i get first the 3 little platys or the 2 bigger gouramis?

and is 3 platy's (2inch) and 2 guoramis (dwarf, 3 inch) to many fish for a 12 gallon tank?

What order to put fish depends on their level of dominance. Introduce less dominant first, and then more dominant because the dominant species won't have an established territory to defend yet--which means they're less likely to attack other fish.

I would put the platy fish in there first to help cycle the tank. Platy are amazingly sturdy fish in my experience and are peaceful tropical community types. They will NOT bully or otherwise attack your other species of fish (though they will do so to theirselves). You do need more females than males, or else the males will constantly harass the females and it could potentially kill them. If you're getting 3 platy, go with 1 male and 2 female, or all 3 female or all 3 male. You can tell the difference by looking at the bottom fin closest to the tail. If it's a rounded triangular shape, it's a female. If it's angular and pointy at the tip it's a male. If you want them to breed, you'll need to add NON-IODINE and non-chemically treated salt to the water at the ration of 1/2 tsp. per gallon.

I would then add the gouramis. Since you're getting DWARF gouramis, you should have no problems. They too are peaceful. People appear to think you're getting opaline or other varieties of gourami which DO get very large and are semi-aggressive. - DWARF GOURAMIS ARE PEACEFUL -. People should do their OWN research before trying to give conflicting advice to others: