Hi Xandu, and welcome to the best Space Strategy game ever (And to the community
). Some humble answers:
A) That depends on you game style. SE4 is very flexible, and the racial techs are very well balanced to improve certain strategies. If you are aggresive, for example, organic tech have excellent weapons.
B) If I understand correctly, no (But I'm not sure)
C) Enough to keep you playing and playing and playing...
I have not downloaded the demo because I don't want to break the surprises
But the 100 turn limitation prevents to achieve the highest levels in science, so you have no access to most weapons and facilities.