Personal view would be no to tetras or danios, they are nippy and first problem will be introducing them other problems may crop up down the line with either dead tetras or a fin nippedbetta. (One point you also need to be aware of bettas have different tempraments meaning some will take tankmates and others will kill anything in sight so have a back up plan). As to platies unsure...but they get relatively big?? But then again perhaps try it but be prepared for consequences. I have 8 male bettas in total in their own domains, some will take tank mates others definately wont.
Tankmates I have been successful with to a point and seen others recommend are African Dwarf Frogs, Pygmy Cories, Javanese Rice Fish, Normani Lamp Eyes, White Cloud Minnows, Apple Snails and Shrimp.
Danios and most common tetras are really bad choices of tankmates for a betta. They are fast nippy fish and will most likely shred your bettas fins . Also becaue they are such active fish, tetras and danios really need more than 10 gallons despite their small size, as they like length in a tank to really zoom up and down .
Bottom dwellers and shrimp are safe cmpanions for a betta. You may want to try a few Endlers or Lampeye Killifish, but make sure you have a spare 5 gallon tank as a backup for the betta in case this doesn't work out.
Lilacamy - White clouds are a cold water/sub tropical fish who thrive better at temps of 18-22 C and should not be kept in a tropical tank with the high temperature of 26-28 C a betta requires.
How big is the tank that we are looking at Jdsworld8? In a small tank I would tend to agree that a danio and many of the tetras would be hazards to an overdeveloped man made betta. Some of these poor fish have trouble swimming because they have such huge fins and that makes them victims when it comes to fast fish in a crowded situation.