Thistledown padded armor has ASF 0% and a max Dex of 10 so it's a good mundane option for a rogue/arcanist. There's other options (Twilight Mithral Chain Shirt, Mithral Buckler) for lower dex characters but they are more expensive.

The Immediate Magic ACF is pretty much only really worth it for Conjurers. Abrupt Jaunt is great. Skillmonkeys do get a lot out of familiars though so you may want to spend your 3rd level feat on Obtain Familiar. You can later take Practiced Spellcaster to negate the CL loss from Unseen Seer, too.

Using your crossbow to do damage is possible, but don't expect miracles. Crossbow archery is pretty feat intensive to really get anywhere. If you're content plinking away with normal Sneak Attack (and maybe Hunter's Eye once you get advanced learning) you don't really need anything except Rapid Reload/Hand Crossbow Focus.
You can get the same effect without spending a feat by using a wand of Ray of Frost or a similar ranged touch cantrip though.