Rachibaby - we see similar behaviors with our DS4.5. I feel like we've been telling him every day for 2 years "please wait your turn to talk," "stop ordering and be polite" or similar. He is always interrupting and often rude.
As for alone time, do you have lego batman, lego star wars, or lego indiana jones? Those were great lifesavors for me when i needed to get some work done or when i was sick or needed some peace. I know it's not the greatest thing to recommend a video game, but the kids are using some thinking skills to figure out some of the puzzles, and fine motor, blah blah blah...
On the being first in school. I wonder if it's anything similar to my son's preschool rituals last year. He had to say "i love you mommy" each step he took on the way to the preschool door, and hug me a certain number of times. if he didn't do his familiar ritual, he'd have a tantrum. Maybe your son is just trying to have one thing the same every day (being first) as a sort of security blanket. What worked for us was finally saying to DS that he had to get all his hugs/i love you's etc done before we entered the building. I made it a rule, and it worked. Maybe it's nothing like this situation but thought i'd throw it out. I'm not sure how you could solve it - maybe there's something else he can do that is comforting that he can get out of the way before the school grounds. ?
