You can auto-bracket up to 9 individual frames, but the maximum increment you can use is +/- 1-stop. So, to get -2, 0 and +2 you could set the auto-bracketing to shoot 5 frames giving you -2, -1, 0, +1, +2.
Whether it's better to use 3 shots or more is dependent entirely on the circumstances, how much dynamic range (DR) there is in your scene and your own requirements. The more DR, the more bracketing you may require to fully capture it all. Lower DR scenes may be sufficiently captured (for you - others may want more or less - it's a very subjective thing) with only 3 shots.
Not sure what you mean by
what sequence should I use
If you're referring to whether or not to shoot the -ve frames first etc then I just leave mine on the default which I think is 0, least exposure to most exposure. It works for me and you should find out what works for you.
For lots more information, the
first few hits are excellent places to start digging for information and don't forget TP's got its own
Post Processing & Image Editing forum which makes a good place to find past HDR discussion
