About c being constant and interaction at c.

You are trying to explain Einstein's second postulate. Since it's a postulate, it doesn't need an explanation. We only need to determine if it is consistent with reality and it is.

 

Arguments don't apply to postulates. You need to understand that.

 

I think the best way to "feel good" about the second postulate is to draw a spacetime diagram with radar and/or light signals traveling at c and use the Lorentz Transformation process to make another spacetime diagram for the same scenario and note that all observers continue to see exactly the same things and make exactly the same observations even though the radar and/or light signals are also traveling at c for different distances in this new spacetime diagram.

 

I don't understand the last part... but next you seem to agree that the speed of the source has no effect on the speed of light, and also very little effect on the speed of particles that are emitted at almost the speed of light.

If with "reduced interaction" you imply that an emitted particle from an object going at almost the speed of light acquires nearly no additional momentum and energy, then definitely no, that's wrong.

There have been hypotheses according to which the speed of light is a limit speed because at that speed there is zero force to accelerate a particle. That was debunked by demonstrations such as the Bartozzi experiment.
https://en.wikipedia.org/wiki/Bertozzi_experiment#Bertozzi_experiment
It confirmed that the kinetic energy of accelerated electrons continues to increase as expected, even with little increase in velocity. Although the acceleration method differs from yours, the effect can hardly be any different: as far as we know (and based on uncountable observations) kinetic energy does not depend on the acceleration history.

 

This isn't about sr exactly, and I don't mean to divert attention away from the sound and important posts above, but I've been struggling with the idea of the postulate of consistency of light in vacum being done away with in gr as mentioned in the popular book authored by Einstein called simply Relativity. I think the argument for dropping the postulate was that because light bent in gravity fields globally or on a large (at least planetary) scale of view, that the principle could no longer be maintianed. Yet when reading the about local regoins in the gr section in On the Meaning of Relativity, I see that they discuss the exact value of the speed of light beinging maintained mathematically in local, regions of spacetime even with gravity, if my read was correct. So is it that c as the speed of light as constant and very important number is not maintained as that exact number in all situations, but is in the regions or special cases when gr is reduced to sr? In my reading of the book Relativty, my impression was that while the rule that in curved spacetime, nothing exceeds the speed of light, not even information, but, yet that what this number is as a numerical value changes ever so slightly because of non Euclidean geometry.
Also, I think in general that while a postulate doesn't need explaining, that looking for new ways to give a reason for known facts is very useful in theoretical pursuits and the development of new ideas.

 

With local measurements the speed of light is still c. However, what Einstein hinted at is that a light wave can only bend due to a speed gradient. See http://en.wikipedia.org/wiki/Huygens–Fresnel_principle. As a matter of fact, Einstein used the Huygens principle for his prediction of light bending around the Sun. No doubt he had that in mind when he wrote the passage that you read. If you need more explanation, please start it as a separate topic.