Process of inperson interview after dropbox appointment

hi
I have some questions and seeking answers here.
I am planning to go for dropbox appointment for my visa stamping with my dependents. In my DS 160, i have selected Mumbai Consulate. however i can book appointment for chennai only. after dropbox appointment if they call me for interview my question is

  1. do we need to book new appointment? OR they will provide me date? and time?
  2. Will i need to go to Chennai for Interview or Mumbai?
    Can any one guide me on the above
  3. my minor will turn 14 soon do we need to book appointment for her ?
  4. Will there be isssue if H4 dropbox appointment is ahead of H1 drop box appointment, as there will be no valid h1b holder visa to provide for h4 applicants?
    Please provide input who had been to these situations.