WELCOME! I tried to answer your questions. If you have any further questions, don't hesitate to ask. :D
If your betta doesn't like the shrimp he'll eat them. :) Snack time for him. Don't be surprised if one goes missing, or all of them. It's fine though.
Neons generally need a larger area to swim. I personally wouldn't put them in a 10 gallon.
ADFs also like to be in pairs.
As far as platies, I think they'll be fine with your betta. You'll just have to watch them in case they start getting nippy though. Most bettas will be okay, especially since they'll be in the tank first.
The more plants the better. More hiding spots, more natural filtration, looks better! You really can't lose adding more plants.