What else do you plan to have in the tank? Female bettas do need space - and will need plants and caves to hide in. In that tank I would say 4. As long as there's nothing else going in the tank with the female bettas.
You will also want to have alternative housing arangements in case the females don't get along with each other. You may want to do some research on setting up a sorority tank.
I would say around 6-8, the reccommended maximum for a 10 gallon is 6, however some people have successfully kept 8 or 10 (tank would be heavily planted though), so with the extra two gallons you have to play with I wouldn't go with anymore then 8 IMO. If that made any sense
I think i may go for 5-6 girls and maybe some oto'sor shrimps or maybe some cories.The tank will be planted and may hav a big tree stump in aswell.how many shrimps,oto's or cories would you have and what do you prefer?thanks!