anesthesia is currently 1+3 in terms of years. before you embark on 3 years of anesthesia training, you need a year of internship. this is typically prelim medicine, prelim surgery, or transitional but some others are acceptable (OB/gyne, peds, FP). the
ACGME website has a link called "Program Requirements" where you can get a PDF that has the exact requirements. the intent of the internship year is to make sure that you have a foundation of basic clinical knowledge before you lock yourself in an OR behind a drape for 3 years.
some programs provide that intern year (4-year/categorical programs) while others thumb their nose at you and tell you to go find one yourself (3-year/advanced programs). The ASA (at least I think it's the ASA...) is now promoting that all anesthesia residencies become 4 year programs where the clinical base year/internship is integrated; there is also a movement to increase the number of ICU months from 2 to 6 over the next few years.
as for hours, it varies. some programs brag about averaging 60 hours a week, while others have reputations for working residents like dogs. of course, the ACGME now limits residents to working 80 hours per week. i don't think most programs average more 70 or so hours per week tops. remember, anesthesia is one of the few, if not the only, residencies where you get your post-call day off (when you're in the OR. all bets are off in the ICU). in the OR, i would say your day typically starts between 6 and 630 in the morning, and ends anywhere from 3 to 6 on average, depending on the program.
as far as competitiveness, anesthesia is in the midst of an upswing. i would still say that it's middle-tier in terms of competitiveness though. i think rad onc, derm, ortho and ophtho (and rads this year) are more competitive. i have no idea what board scores you need these days...