I would go with the current standard and do the 'all-in-one' psych residency with the normal PGY-1 year at the same institution that the residency is. This allows the advantage of getting to know the intracicies of the hospital, the personnel, the psych faculty earlier, and more inpatient exposure, which is aggravating at times, but helpful.
Then after all that, you have to scour the country looking for PGY-II slots open for psychiatry. I'm not sure it's worth it from the beginning.
To address your second question: I'm not aware of any three year psychiatry residencies.