Correct. It is called the equivalence principle. You can arbitrarily pick any point and call it fixed.
Also, saying there is 'no absolute frame of reference' is an assumption of GR not a demonstrated fact
Correct, science has no facts, just evidence.
And, GR does not require that the speed of light be fixed across time, only that it be the same throughout the entire universe at any point in time. That is a huge difference in meaning. If the speed of light is not fixed across time, then time and distance are not variables.
No, even if the speed of light isn't the same at all times, time and distance are still variables. You have just added a third variable.
If you performed an experiment to detect the assumed motion of the earth about the sun, found no sign of said motion and then developed a theory that assumed that motion but had to be consistent with no evidence for it, you would have GR.
You will have to explain yourself a little more. I have no idea about what you are trying to say.
And again, let's not assume that ease of use represents reality because then you would have one reality within the earth-moon system and an opposite reality within the solar-system. That you choose to believe the solar-system CS is a philosophical choice, nothing more.
A philosophical Choice? It depends on what you are studying or attempting to do. If you are planning a trip to the moon, you can use the Earth as a fixed reference point. If you are studying the planets it makes sense to use the Sun as a reference point. If you are studying the stars it makes sense to use the stars as a reference point. It is all relative.
That's what Ellis was saying.
I don't know who Ellis is.
What you guys fail to understand is that a huge number of things you accept as fact, are not.
There are no facts, just theory and evidence. Find some evidence to contradict the theories and you will invalidate them. That is science in a nut shell.
"People need to be aware that there is a range of models that could explain the observations, Ellis argues. For instance, I can construct you a spherically symmetrical universe with Earth at its center, and you cannot disprove it based on observations. Ellis has published a paper on this. You can only exclude it on philosophical grounds. In my view there is absolutely nothing wrong in that. What I want to bring into the open is the fact that we are using philosophical criteria in choosing our models. A lot of cosmology tries to hide that.
Ellis, George, in Scientific American, "Thinking Globally, Acting Universally", October 1995