You can change in user or server attributes. It has been discussed many times. Search.
Color has nothing to do with satellites or ignition. It's network connection status. There's a configuration option to disable offline state. Search.
Same answer as 1.
2.2. Is it possible to make the units appear as red when there is no ignition on and green when there is ignition on? instead of looking at network status.
If you are asking if something like this is available out of the box - the answer is no. But the source code is open, so of course you can implement it.
The speed is displayed in knots. can you change it so that it is in Kilometers per hour?
Some of the units switch between green and red all the time because they are indoors and have very few satellites and therefore they jump a bit in the positions so traccar thinks they are running (green)
Can it be made so that traccar is not so sensitive? Perhaps start and stop can be detected on ignition on, off. so if there is no ignition on then it will always be red.
It is also best on machines that often stand in the same place and dig for example.
Can I change the hours and kilometers on each unit in traccar. ?