boys can be quite tricky little things can't they? Very different from girls, I know is a generalisation, but it definitely seems that way - I can't help notice that raising my sons is a whole different ball game to my family/friends daughters. For example, the girls sit happily and coo over their toys at the table and the boys yell and clamber over the toys to do some illegal gymnastics on the table top! Different animals altogether!
I really don't think we should be encouraging the OP to regard her little boy as "tricky", and to be honest, OP, I'd avoid labelling your daughter as a "good girl". I grew up with that expectation and it isn't fair.
The fact that some posters have boys or girls who appear to fit the stereotype doesn't mean that the stereotype is justified. I have 4 - three boys, one girl - and mine didn't match the rough boy/good girl stereotype. Perhaps that's because I didn't expect them to?
I think it's unwise to send a child to school without breakfast - this will potentially impact on his learning and behaviour. Mine were all keen on writing/drawing/building things in the morning, and it meant we just had to start the day earlier. There was no shouting up the stairs though - I would supervise the younger ones until they were ready to come downstairs and they all helped set the table while I made breakfast. We ate together, and since we were up fairly early, they then had time to play/go to the loo/read before school.
Your little boy sounds lovely. He wasn't causing havoc - he was caught up in writing his story. Let him know he has to sit down to eat, but that his story-writing is important too. I had a dreamy one who got ultra-absorbed in activities and if I'd allowed it, food would have been way down the list of priorities. But I'd tell her "breakfast is out now - come and eat so you can get back to your drawing/writing quickly" and I'd keep talking brightly as we sat at the table - it distracted her and (usually) got her to sit down quite happily.
Maybe tell him this evening that you want all of you to have a nice relaxing start tomorrow, and that you'll expect him at the table when you say - if he is now in the habit of delaying, you may have to bring him down the first day or two, to show him you mean it. In the morning, try to keep calm and cheerful (I know, I know) so he doesn't see it as a battle.