Hey, at least you gave the show a shot before you decided to give your final judgement on it. All I can say is that not every show will appeal to everyone. For example, I also love Firefly like you seem to do but I know plenty of people who didn't care for it at all.
In answer to your questions,
1. The Pegasus was sacrificed because it was the only way to buy the Galactica enough time to FTL to safety. Besides, the show is called Battlestar Galactica, not Battlestar Pegasus.
2. Starbuck was referred to as the "Harbinger of Death" by the cylon hybrid and as you saw in the finale, she did indeed lead humanity to its end. She instead brought death to the cylons.
Here is the full prophecy from the hybrid in "Razor",
Kara Thrace will lead the human race to its end. She is the herald of the apocalypse, the harbinger of death. They must not follow her.
3. I do agree with you that Helo (Karl Agathon) got off way too easy for disobeying the orders of Adama by botching the plans to wipe out the cylons with the virus.