1) only if you want to store the preset registration and tempo associated with that variation as a convenient starting point, otherwise you can just select any pattern and store in panel memory but for example the tempo you have at that time on the panel may be unsuitable for that style.
2) no, if you are referring to the various workshops in my book, doing this just sets up the conditions later to evaluate the new composer at a suitable tempo and registration etc once it has been created.
3) a style can be named and each variation within it can also be named. Since one touch play is obviously the default variation 2 setting of any style, the name is the same as that seen when looking at the style in the Music Stylist Category lists, i.e. second in the group of 4 variation names for that style.