1) Tagged through.
2) Get the BPs at the transfer desk in the terminal.
3) I like the views from the upper level (follow signs for lounges) near the center of the "Y" of the terminal. Other than that, grab a snack and try to not sleep through the connection.
4) It is not luxurious. It is not torture. UA doesn't offer premium economy, just some seats with extra legroom. Only you can decide if that's worthwhile compared to the cost.