1. Unknown if you violated the setup and hold times. you could get a 1, 0, runt pulse, toggle...anything goes.
2. walk ones/zeroes/patterns through the memory via writes, then read back and verify.
3. that's more complicated, but you should do it synchronously. if you are asking these "elementary" questions, you should stick to synchronous designs for now and not be starting and stopping clocks, but rather enabling or disabling pulses that you use the clock to sample.