As season 2 was actually only 4 episodes it was tacked on the end of the Season 1 DVD (Season 1 was 9 episodes). So Season 3 was the first full length season. Don't believe me look here: http://www.imdb.com/title/tt0106028/
Oh and that page will help you answer one of the questions.
From Radio Times:
Homicide: Life on the Street, the cop show which spawned a thousand imitators, is back on DVD in the UK this summer. From the writer and producer of The Wire, the second series of this award-winning show is released as a five-disc boxed set.
Shot through with gritty realism and and nail-biting tension, Homicide captures the daily trials and tribulations of a team of homicide detectives on the frontlines of crime prevention in a manner reminiscent of CSI and NYPD Blues to name but two of its successors. If you're a fan of crime drama, you won't want to miss out
Homicide: Life on the Street series 2 is out now to own on DVD, but you could win yourself a copy thanks to Fremantle Home Entertainment. We've got a copy to give away, as well as a portable DVD player to watch it on! http://www.radiotimes.com/content/competitions/homicide2/