So I just finished UBW on the true route (ending was sad as hell :[). I know there's another ending called the good ending where Saber doesn't disappear right away. Should I bother getting the good end, or is it just a minor change? If it isn't anything too major, could someone please tell me what the differences are?

Also, I thought UBW and HF both opened up at the same time, but at the end it said HF is now open. Does this mean that HF is kind of like closure to the story, and answers all the unanswered questions so far?

Lastly, what was the "Answer" thing that happened after the Epilogue? I wasn't really too sure what was going on. Was it just the battle between Shirou and Archer from Archer's perspective?