I am not a lawyer, but my understanding is that impeachment is the accusation and preparation of articles of impeachment. The vote is the conviction. An impeachment is sort of like an indictment.
Lawyers?
No.
Only two US presidents have been impeached, Andrew Johnson and Bill Clinton.
When you are in a hole, stop digging. You made a mistake by claiming that President Nixon was impeached in 1973. Just admit the mistake and move on. All of us make mistakes, especially when commenting on a live thread.
I'm not a lawyer, but my understanding is that articles of impeachment were being prepared (or had been prepared) but the House had not yet voted on the articles. The House probably WOULD have voted up the articles, so Nixon resigned before the vote.
Your understanding is incorrect. Nixon was not impeached.