I think 1 is incorrect. There are two types of interviews in Sweden. Normal police interviews and 24:8 interviews. The purpose of a 24:8 interview is to determine if it is necessary to arrest the suspect, and has nothing to do with if the suspect will be charged or not. (Though he must be charged soon after being arrested or let free.) So they do only need to have a normal police interview with Assange at this stage. The 24:8 interview should be held once Assange has arrived in Sweden.

Basically the process should be:

  1) International arrest warrant
  2) Police interview in London
  3) Charges are laid
  4) Extradition to Sweden
  5) 24:8 interview to check if Assange is likely to leave the country.
  6) Trial

People with more knowledgeable of the law are welcome to correct me