Will expresses expectaitions and things that are not planned, decided to do them at the time of speaking. Going to expresses things that are already planned.

I will be going to University unless I change my mind, in which case I will not. I am going to University unless I change my mind, in which case I am not. I think you can use either except if you are doing the task. I am at University now studying. I will at University now studying. (makes no sense) Hope this is helpful.

I think that can both express planned or spontaneous actions. With "going" you need a linking verb "am, is are." If you wish to emphasize that the action is sure to occur you would put emphasis on "am" or "will". You can say: These pairs essentially mean the same I am going to be home later. I will be home later. I am going to be 10 next year. I will be 10 next year. I am going to see you tomorrow. I will see you tomorrow. Will you be home later? Are you going to be home later?