1. Tactically, you may want to keep them alive for a while until you kill the flak, etc. Strange strategies are sometimes called for.
2. You can view that if you hover your cursor over your metal or crystal, and in each extractor's tab it shows how many refineries can assist them. A refinery works in every extractor in that gravity well and the surrounding ones.
3. You can have your units hang around a sun, or you can research antimatter capacity and regeneration upgrades in the military research tab. They're fairly high-level though. Advent also have a structure for that.
4. You get an artifact by exploring a planet (it works like a planet upgrade) and sometimes you can find other handy stuff on a planet, like a trade boost. Not all artifacts are in every game though.
5. If you select the factory or the planet it is hanging around then there should be a circle with yellow arrows pointing to the center. Hover your cursor over it and it will tell you where the waypoint is. You can right click it to cancel any waypoints or click on it and then click on somewhere else to get it to go somewhere. If you set the waypoint to a fleet, it will move to that fleet as quickly as possible and join it.
6. Both factories will work together to churn out your units as quickly as possible.
7. That shouldn't be too hard with the empire tree, or just zooming out and clicking on your units in that circle around each planet.
8. The TEC and the Advent have an ability to capture tied to their colonization vessels. The Vasari do it with their scouts.
9. There is research in the civics for all races that increases your extractor output.
Hopefully that helps.