I'd suggest avoiding the Pathfinder Society set at this point as it was geared toward the card game more than for those of us trying to use PFS in our tabletop games. You should be able to run the bulk of the encounters using the sets you have purchased. If you want to add more Golarion specific factions - which does include Pathfinder Society pawns, then you should add the Inner Sea Pawn Box. If you just want a wide variety of NPCs to fill in the blanks on your table, then the NPC Box is the way to go. In the long run, both are useful in Golarion based games.
It's been a point of contention amongst those of us that were looking forward to the PFS set. Apparently, they do use pawns in the ACG sometimes and this set was meant to appeal to them. Many classic scenarios and NPCs for PFS were ignored all in an effort to make a set for the card game. It's a simple choice really. You can look at the pawn list and decide if it works for you or not. If you're just starting to build your pawn sets, it is a good set to buy, but you'll see repeats from Bestiary 1 and the NPC Codex Box.
Pawns are not generally used in the card game. Too hard to shuffle.
I can imagine using pawns or minis in place of token cards to keep track of which location you're in (I've done it), but that's all.
I talked about it in my review and it's been mentioned several times elsewhere on the PFS pawn set product page. Paizo dropped the ball on what should have been an indispensable set by trying to appease two masters and in the end appealing to no one.
Inner Sea has all of the Golarion factions which is really cool. The summoner set is good for filling in the blanks on summons, but has a lot of crossover with the Bestiary sets. The Monster Codex is an army builder for those races: orcs, lizardfolk, vamps, drow, etc.
If you're into do-it-yourself and have a color printer, you might want to check out the Paper Minis for RotRL and CotCT. I have the Sandpoint set and the Edge of Anarchy set.
You print the Paper Minis onto cardstock and then fold and glue them together.
Alternatively, you can print them onto paper, glue them to a piece of 3mm white foam sheet, and use standard pawn bases for them. Instructions for making pawns like that are at this link.