In a 10g tank with that selection of fish, the worry isn't the bioload as much as it is the territory needs. You don't want any of your fish to be too crowded. I personally don't see a problem with 2 platys, one betta, and 3 cories as long as you make your water changes priority. Also, how is your filtration? A wise woman once told me its OK to slightly overstock if you have a filter that is rated for a 15 or 20 gallon tank. The thing with cories is that they stay on the bottom level of the tank most of the time. You want to plan a tank with fish that are top-level dwellers, mid-level, and bottom level. Your platys are your mid levels, and your cories are your bottom level. Then you have your one betta female, the only one that has territorial needs.
ALSO! If the tank is cycled, and you want to make sure your water levels aren't getting too dangerous, make sure it is planted to help with nitrAtes. Hope this helps! :)