I think the APG would be available - it wasn't stated either way and the DM has it. I'm definitely interested in this shadow build - will do my research.
i know you said you like multiclassing in Pathfinder, and bully for you that you do!, but one of the things
I like best about Pathfinder is that it is easier to pull off cross-class "roles" without actually having to multiclass, particularly as compared to 3.5.
Using 20 point buy (as it looks like you are), one possible set of stats would look like this after racial modifiers:
Str 8, Dex 14, Con 12, Int 14, Wis 14, Cha 16
With the favored class bonus going into skills (and a set of masterwork thieves' tools), at 3rd level you would have:
Disable Device +8, Knowledge (arcana) +8, Perception +7, Spellcraft +8, Stealth +12
Not as good as a "real" rogue for certain, but still pretty functional!