Difference between 360 extra high profile and 460 extra high profile? Does the base get wider?

The base diameter of the implants has to be less than the diameter of your breasts, so the extra high profile is the largest implant for a given base width. If you want to go larger and your breasts can accommodate it, then the same profile implant in a larger size will be both wider and more projected.

It depends upon the the Brand.  I looked up the implants offered by Natrelle (Allergan) and clearly the base widths increase.  After 285 cc implants, for every incremental increase of volume, the base increases by .25 cm.  I would assume that your implants would do the same.

There are many different styles of implants, they have different names from every manufacturer.  The basic round implants (not shaped or anatomic) have 2 dimensions, base diameter and projection (height).  For the different styles the base and projection change, each getting larger with increased size.
In this situation with the extra high profile style implant, the base diameter changes about 1.0 cm for every one hundred cc's and the projection changes about 0.5 cm.  That is where the extra volume goes.  Hope this helps.
Good Luck!