Frontierland is where the parade starts, I have never tried to view it from there, I would guess by Pecos Bills maybe. We have viewed the parade from just in front of the Hall of Presidents right by a turn. It was a good spot but doesn't come close to Main Street, the snow and lighting is better.
How early really depends on what day of the season you are going. We have noticed that even the middle of December can be quite busy. Last year we went at the end of November to the first week in December and both parties we did were busy with one being sold out. On busy nights we try to get there 45 min before, but once again this applies to Main Street. If it is a slower night, which we haven't seen in a few years, we could grab a spot about fifteen minutes before the start of the parade.
There are two parades per night and the second one has always been less crowed for us. This use to always apply to the Boo-To-You parade also, but there has been a few times for us when it seemed just as crowed as the first.