Acela costs like 3x to 5x as much, saves about an hour at best. Generally nicer experience, with nicer assigned seating, less stops, and a quiet car. The regional is fine, just slower and makes more stops.

Baggage works like any other train, you bring it on and there's a rack for suitcases + overhead space. You can bring two suitcases + two carry items.

Worth signing up for the Amtrak rewards points and using your number when you buy tickets. The Acela especially gives a lot of points, and you can easily get enough for a trip to Maine if you take it regularly.

Ultimately the best way to get to NYC I think, more comfortable than the bus and less headache than flying. They all take about the same amount of time, but the train is the most comfortable and convenient.