I know when I show up to vote they have my name on a voter log for the place I'm supposed to be voting in. I don't know if I could drive some other place and vote again without my name being on their list.

The Answer is yes, but its illegal.

all of them, there is no national voter database

some states probably have laws prohibiting you from registering to vote if you are already registered somewhere else, but there are likely no mechanisms for them to investigate or enforce

1 person 1 vote. Anything else is fraud.

There is one exception. The democrat party utilizes super delegates whose votes count for more from some people. Don't believe me... Look it up.

I can answer one of those questions. When you're a dead voter, you can't drive to Ohio and PA to vote in both on election day. Living people can possibly do this, which means they have more voting power than dead people. This is why mail in ballots are so important - they help prevent dead voters from being disenfranchised.

It's just a "glitch" in the system when multiple ballots are sent to the same person, like the 83 received by one person in California.....
https://www.dailymail.co.uk/news/article-3902690/Questions-voter-fraud-man-finds-83-ballots-shipped-single-address-apartment-complex.html

In theory, no, it is illegal. In reality it probably happens a lot as I doubt States talk to each other.