Charging and the trial date being set are irrelevant. What is relevant is the custody time limit. More info here
http://www.cps.gov.uk.../custody_time_limits/
Prosecution will normally have disclosed the full file to the defence by the time of the plea and case management hearing. Thereafter the time limits in the Criminal Procedure Rules and CPIA 1996 apply with regards to primary and secondary disclosure.
The defence solicitor will always discuss the prosecution bundle with the client. The client needs to know the case against him. The lawyers need to know what defence the client is running - ie "wasn't me, I have an alibi", "self defence" etc. All these will be discussed in interview with the client.
The link Markrae has provided deals with the difference between solicitors and barristers. However, for a very serious case, such as a murder, Counsel will be instructed quite early on so he can advise on all aspects of the defence (the same goes for the Crown).
A defence case statement is the document which sets out the basis of the client's defence.