In general when a stat block lists a "+" it is a spell adder and when it lists a "x" it is a multiplier. For RMSS it really depends on what other PP bonus items are in your game and how you want to deal with them going forward.
For example I have often gives out a x4 PP item for specific spell lists, specific spells or for base lists with the knowledge that it is a very special item. In general I do not have has many problems with + items vs x items. Also in general I have reduced the standard x items to things like x (1.5, 1.75, 2, 2.25, etc) and that preserves the flavor of x items without getting too out of control on the PP side of things. Also by having some restrictions on when the PM bonus items can be used or how they are used adds flavor and some restraint, IMHO.
Unfortunately I do not know enough about SW to help you out with the other questions.
MDC