Although Criminal Damage can be serious enough to be dealt with by the Crown Court, it would be unusual. From what you say it sounds as if the CD charge resulted from bad behaviour at the Police Station and is probably not serious (as Criminal Damage goes).
That being the case, the excess alcohol is the most serious offence. For a third offence (presumably within 10 years) custody is a distinct possibility, even if the alcohol reading was comparatively low. The maximum for the offence is six months and if your friend pleads guilty he will receive one third discount, making the maximum four months.
Unless the court has access to a recent pre-sentence report, one will be required before sentencing (unless only a fine is proposed � and that is extremely unlikely). A lengthy period of disqualification will also be imposed (a minimum of three years, but possibly longer).
Finally, despite what has been said, what time of year it is or what mood the magistrates are in will have no bearing on their decision. Magistrates (and indeed judges) are bound by law to follow a structured approach when sentencing. Incidentally, lay magistrates are unlikely to have had a �pig of a week� � at least not on the Bench. They sit only on a part time basis and it is unusual for them sit more than once in a week unless they are involved in a lengthy trial.