I got 5 neons
1 betta
4 sterbai cories
Its an 18 gallon or 70 litre if you wish.
Ph is 7.6.
Temperature is 24-26 Celsius
I wanna add say 4 more, or will that be over stocked?
You could do 3 neons and 2 cories.
You could go with 5 Harliquin Rasboras but that may be pushing it. You could also consider adding Endlers or Least Killies.
I think the harlequins would be a great idea. They also aren't going to push your tank to being overstocked.