'Self defence' won't stand up in law if there is evidence that the defendant used more than the minimum amount of force required to ensure his own safety. For instance, if someone throws a punch at you and the only way that you can prevent him from throwing another one is to punch him back, that probably counts as 'self defence'. However, if that returned punch knocks your assailant to the ground, you must immediately cease punching or kicking him. (i.e. you've given yourself enough 'breathing space' to run away, and that's what you must do). A second blow from you constitutes assault. If there is any evidence to show that the defendant's actions were 'excessive' he would be well advised to change his plea to 'guilty' and to seek to use 'provocation' as a mitigating circumstance to reduce the sentence imposed by the court.
It's theoretically possible that a 'drunk and disorderly' charge could be added at a later date but, in practice, it's extremely unlikely that the CPS would bother adding such a minor charge when a far more serious one is already to be heard before the court. However, that doesn't prevent the CPS from bringing evidence before the court to show that the defendant was drunk.
You haven't stated why the case has been transferred to the Crown Court. This might, of course, simply be because the defendant has elected a jury trial. However, if the case was referred to the Crown Court by the magistrates, this indicates that the magistrates are of the view that, if the defendant is convicted, their sentencing powers are insufficient. (i.e. they believe that a custodial sentence, exceeding 6 months, might be appropriate). It should be remembered, though, that the magistrates had not heard the full case. (For example, they would be unaware of any element of provocation involved). So it doesn't automatically follow that a lengthy custodial sentence would follow.