I think democrats would, for the most part. Perhaps less enthusiastically, but since they hate Trump, I think it would not be a major issue.
The question is, how would low-information unaffiliated voters respond to having a socialist in the ballot? This is a difficult question to answer. Traditionally socialism is a bad word in US politics, albeit less so with younger voters.
Personally I don’t really buy the “Bernie would have won” stuff but there’s really only one way to find out.
No. I think it’s a pretty shitty thing to do unless you had a reason to feel unsafe, which I personally never have.