Can we set maximum number of photo of each Album??
Can user create their own group for read only? And the user can't read other username in permission mode.
As of 1.4.4pl2 there isn't a way to set a max number of photo's for each album. However I believe this will be in versions 1.4.5 or 1.5. I'll get that information for you.
For your second question I'm not really sure what you mean. I believe as of right now (1.4.4pl2) the only way a user could could create another user is if they have admin rights.