I think you can take the test once every calendar month. So even if you took a test on Nov 29th lets say, you should be able to take the test again during the first week of December. Its better to double check this with the ETS people. I think they only allow you to take the test twelve times every year (Although I wonder if anyone would go that far).
Most of the Universities require GRE schools these days. I have yet to hear about one that doesn't require atleast a general test. However, a lot of schools (usually the less competitive ones) don't have a minimum score for GRE and taking the test itself would be sufficient.
Also, it depends on what program you're applying to.If you're applying to Science/ Engineering related graduate programs, then you should aim to do well on the quant section. Otherwise, if you're going for Social Sciences or Humanities, then verbal score becomes more important. Although I don't really know the cut offs for these. Maybe someone else could answer this.
I think TOEFL is far easier than GRE. The vocab section in GRE is pretty tough to crack and it even makes people, who are native english speakers, sweat. However, I think its comparable to SAT general test.
