Beam me up - trying to get a basic understanding of GR

Trying to understand SR and GR at a basic level, I've read around on the web
and now have questions I can't find answers for. Being new to this all, and
having only physics 1, I may be inadvertently resurrecting dumb questions, but
if someone has the time and inclination to work with me on this I'd appreciate
some answers to these questions.

What I seem to have found so far:

1. SR is invalid. Inertia, motion, aging etc. depend on the locations of masses
around us in the universe. There is an absolute frame of reference, the
universe. (Whether it is infinite or not we don't know.)
2. GR replaces SR. Some say that it works because it takes gravity into
account, but some say it is also invalid, either logically inconsistent or they
point to a math flaw.

Some questions I have now are:

a. If you agree that SR is dead, can you explain how GR avoids the bullet that
killed SR? I thought that GR ADDs the space-curving effect of gravity to SR?

b1. GR also states, like SR, that time dilates
How can time dilation explain the measurement of light speed as c in both
the cases of a spaceship approaching and departing from the light source at
near light speed? Surely in one of the cases time dilation is an exacerbating
rather than mitigating factor?

b2. Imagine two space-stations ST1,ST2 exactly one light-minute apart in their
frame of reference, and two space-ships SP1,SP2 travelling at near-light-speed
also the same distance apart, approaching the two stations along the same axis
on which they lie:
ST1. . . . . . .ST2 <-SP1. . . . . . .<-SP2
When spaceship SP1 is alongside ST1, and SP2 alongside ST2, spaceship SP2
flashes a beam of light towards ST1. The light reaches ST1 in one minute
('static'-time). Spaceship SP2 reaches ST2 a second or two later than the light.
b3.1 Does SP2 perceive the distance between ST1 and ST2 to be as far as we do?
b3.2 How many of SP2's seconds does it take the light to reach ST2?

c. Is it possible that we can use SR as a useful approximation, like Newtonian
physis, under limited circumstances?

d. Are there situations in which GR is known to be experimentally dead wrong,
and if so, do we use GR as a useful approximation, under limited circumstances?
.