On the additional witnesses (FYI, witnesses were called in the house and admitted into evidence into the trial, so yes, I do mean additional), I listened to a Podcast today with Ted Cruz and Lindsey Graham that made some very good points on why the vote went the way it did.
The main point was that regardless if what Bolton said was true, the president is still allowed to investigate perceived corruption. So there was nothing Bolton could have testified to that would have changed this, especially considering Bolton alluded to 2016 interference being the cause for the requested investigation, not for a 2020 advantage.
Second was that the Dems, especially Warren, made it impossible for either Lamar Alexander or Murkowski to vote for witnesses, creating a 50/50 split. Alexander, who is an institutionalist, was pretty much a no vote early Thursday for the pure reason that he did not want to put the Senate into a position to make judgements on the law for the first time ever, instead of the courts. He wanted to preserve the institution as much as possible. However, Murkowski at this point was still up in the air.
Then Warren sent in her question asking if Justice Roberts, along with the Supreme Court, should be embarrassed by the proceeding, and it became obvious that if a 50/50 vote happened, regardless if Roberts declined to vote himself or voted for no additional witnesses, the Dems would use this as a way to delegitimize the Supreme Court. This enraged republicans much more then what the Dems anticipated and it was at this point that both Alexander and Murkowski decided it would be best to have a 51/49 vote so the Dems would not be given the opportunity to destroy the legitimacy of the Supreme Courts (along with everything other institution they have demolished since 2016).
Essentially the Dems, especially Warren, helped push the Republicans towards this 51/49 vote.
