Helo,
I'm thinking about my next character: a sylph sniper/spell sage going for the arcane trickster prc. Of course, it involves the cloud gazer feat, which allow you to see through three square of obscuring mist, sneack-attacking everything from the fog.
I think about making him a spellsage, because I play in a small party (3 characters), often lacking full-casters (our current group include a paladin, an alchimist and a magus) and the healing/recovering spells you often need after combat. Plus our campaign are usually low cash and low magic, so we don't have tons of wand of cure light wounds, nor raise dead available with discount in every church. The sniper archtype gives me a 40 feet range for sneak attack, which may be usefull before I get those damned sniper goggles.
For the feats, I would like to take the whole sylph package :
lvl 1 - airy step
lvl 3 - cloud gazer
lvl 5 - ?
lvl 7 - ?
lvl 9 - wings of air
lvl 11 - inner breath
So, I don't know which feat to choose at lvl 5 and 7, nor which rogue talent to select (dampen presence seems attractive, against those foes who have blindsense and blindsight, but sniper eye could be usefull as well).
As for the traits, magical knack and wind carried voice.
Any suggestion for the feats, and spell selection or warning (maybe I'm doing something wrong ?)
I will probably aim for 18 Int and 18 Dex, str and Con 10, wis 14 and cha 8 (the shy assassin type...).
One thing to consider with the arcane trickster is that sneak attack can be applied to ranged touch spells by the simple rule that they require an attack roll and they deal damage. Tack on the fact that the arcane trickster has abysmal BaB progression, this means that you'll be wanting to target their touch AC whenever possible. Even a ray of frost used as a standard action, with your BaB, might have better dpr than a full attack with arrows, because your BaB isn't even going to hit 6 until level 11 with 3 levels in rogue.
With that in mind, whenever I consider an arcane trickster build, I like to minimize my investment into martial classes by taking a single rouge level (or something that gives sneak attack at level 1, like the vivisectionist alchemist) and then taking the "Accomplished sneak attacker" feat.
With this method, you can begin taking arcane trickster levels as early as level 5, after qualifying with 1 level in sneak attacker class and 3 levels in wizard.
That's just my take on arcane trickster, though. Other than that, you have the right idea in building to create situations where you get sneak attacks. Glitterdust blinds enemies that would otherwise see you, greater invisibility is always a spell you should take, and the arcane trickster has very powerful options to help you sneak attack should all else fail.
With that in mind, whenever I consider an arcane trickster build, I like to minimize my investment into martial classes by taking a single rouge level (or something that gives sneak attack at level 1, like the vivisectionist alchemist) and then taking the "Accomplished sneak attacker" feat.
I did not knew such a feat existed... Food for thought, even if I do like evasion a lot (breath weapons monsters and fireball are a problem when you are hiding in a cloud...)