Well, as teg21 said it depends on the snake. They each have their own mood. But ill say this: its been one hell of a joy to work with my blood so far. Mine has never actually struck at me other then in the pet shop when were probing the poor girl.
My snake personally is calm enough. I can take her out for 2-3m now without a problem and she will just sit there. Anything more and she will start moving about so i put her back. Its getting better, when i started handling her 2 weeks ago i could only have her out for about 30 seconds and that was with massive hyper ventilation.
As for size, well scroll down - the females get massive. It depends on the subspieces i think. Im in over my head here i think, im not sure which of the 3 gets the largest. You got Brongersmai which is the true blood(mine is brongersmai), Breistensteini common name borneo short tail bloods and Curtus Curtus (someone correct me if im wrong) which is the black blood. I believe the largest is the brongersmai. Very large females can get to about 7' but thats rare i believe. Usual size is about 5-6 feet - but they get extreemly girthy.
Its of all importance that you get a captive bread snake - i cant stress this enough with bloods. Dont get a wild caught, specially if this is your first blood.
Bloods are special snakes, not only because of their special apperance but they, to me at least, seem smarter then corn snakes.
Anyway, youre better off asking someone like Angel (gogo151) or Kara (KGL), they know a hell of a lot more about bloods then me.
Sometimes the best teacher is expirience. And they have a lot more then me - at least for now. 
-Daniel
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"From my rotting body flowers shall grow, and i them - and that is eternity."