1, 2, and 3 sound like pretty typical ADHD behavior to me. Don't know what happened to 4!

5 strikes me as pretty normal for most young kids - all my brothers did this. Then again, the two genetically related to me were also diagnosed with ADHD. My non-ADHD stepbrother was right along with them in terms of silly repetition, though.

6 could be related to multiple types of things. Sounds very much like ADHD behavior, but could also be flat-out personality differences, etc. My mom always said all three of her kids were polar opposites, so it should come as little surprise that your 9-yo and 5-yo are completely different!

It sounds like you have reason to keep your eye on this. There's a known genetic component and you're seeing some behavior issues. Those could be related to ADHD or any number of other things - he might just be "high spirited" so to speak, or he could have allergies that cause this kind of behavior (I have a cousin whose allergy to Red Dye #5 made him act pretty wild), or I'm sure there are other possible explanations.

If you're not having too difficult of a time controlling him and he's not causing major problems, IMHO (and I'm not a doctor!) you should ride it out as long as you can before running to the doctor. I'm sure you know that ADHD is considered way, way overdiagnosed. It could be stuff that your son outgrows, or related to other issues, or it could actually be ADHD. If he's not struggling in school, having social problems, or other issues, it's probably OK to just keep an eye on it for now. If it seems to be causing him or others distress, that's the time to go to the docs. I found that ADHD treatment helps me sleep better, interact better with the rest of the world, and work better - huge relief for me on all counts - but it wasn't really a problem for me until I was about 19, so I didn't get diagnosed or treated until I was 22!