Three suggestions to the guide:
1) I feel you should include a section for advanced firearms. With Iron Gods, these weapons should be easily available. Their are two regions of the map where advanced firearms shouldn't be difficult to justify to most GMs (Starfall up north and Alkenstar/Mana Wastes down south). But are high tech cities where these weapons can be acquired.
2) Add Skinwalkers to the guide, especially the weretiger-kin. +2 Dex, +2 Perception and See in Darkness. See in Darkness is possibly is one of the best ranged abilities in the game. It's Darkvision with no maximum range. You can fire at people with no penalty out beyond the range of normal dark vision and can see in supernatural dark.
3) I have been working on a level 5 build with a friend of mine. You may want to add Ninja to the multi-class. I feel it makes a great gun build as early as level three.
Level 1 Gunslinger/Level 2 Ninja
Deeds (Level 1)
Sneak Attack +1d6
Ki Pool (1/2 Ninja Level + Cha mod)
Ninja Trick: Vanishing Trick (Invisibility)
Feats: Point Blank Shot, Rapid Shot
Within 30 feet, the character can go invisible and pop out making three sneak attack shots and at end of the attack, use a swift action to return invisible. Can be stacked with pistelero for bonus damage, or with sniper's goggle's/rapid reload/rifle for a nasty sneak attack sniper. With invisibility it allows for a handful of easily repeatable triple sneak attacks every day with the number increasing as the character gains ninja levels.