I change my oil by driving conditions not a set milage. For instance if I'm driving mostly city and short trips where car isn't getting to running temp I'll change it alot sooner. If I'm driving mostly highway and at full operating temp I'll extend it. @wintsonvegas said it best if it looks dirty  change it. Another thing you can do If you really want is contact Blackstone lab and get a oil test kit and send it out. They will tell you oil life and condition of engine. You will know for sure what mileage is best for your car . I sent out sample in past and found out 1 car I was changing oil 2500 to soon another car I was changing 1000 miles late. That's was going by manufacturer oil change times. Now I change it by conditions not mileage.To keep it simple if your oil is dirty chany it a little sooner.

Scotty addresses your concerns between 6:45 and 9:10. Personally I think every 3000 miles is overkill with modern GF6 full synthetic. The dark color is normal with synthetic oil because of the superior detergents that are designed to hold containments in suspension. Changing oil at 3000 miles is certainly a good thing for the engine but unnecessary.

Should be fine. The main downside is that every time you change it there is a small chance for small errors that could become big (like not getting the drain plug tight). 

it's supposed to look black. The contaminants should be in the oil, not on your engine.

If your oil looks black change it. I have a 22 year old Explorer and it gets black about 3500 miles and I change it. Like Scotty says, oil is cheap and replacing your engine is not.

I would say every 12 months or 5000 miles.  Do whatever comes first. 

you could split the difference and change it every 4000 miles that is what I do.

Heavy city/hot cold weather, every 3k. otherwise 5k