[rjuvyich] Supermassive black holes

Do objects really experience significant tidal forces near the event horizon of a supermassive black hole?  Because it is so big, it seems the differential force due to distance is minuscule, much like an astronaut orbiting the earth.  But then, what happens when a spinning object partially crosses the event horizon?  It can spin in, but can't spin out.

Is a full treatment of General Relativity necessary in the neighborhood of the event horizon of a supermassive black hole?  I'm wondering, if, if big enough, the space (spacetime) may be locally treated as flat, or some other simple approximation.  In the extreme scenario, if our Universe had barely enough mass to collapse in on itself, then we would be living inside a giant black hole, and space here is locally flat.

If space itself around a supermassive black hole is not that weird, what powers quasars and active galaxies?  What is the matter around the event horizon really like?  It's probably high density.

I'm guessing Dyson sphere or Ringworld of neutronium.  If less dense, stellar fusion (a giant star).  But the structures are not gravitationally stable.