Guide concept help

[Unien]

Hello.

I'm working on some sort of guide concept for my next Runelords AP char.
Usable material (for feats) is limited to Core Rulebook an APG.
Race: Human
Stats (rolled):
STR 11; DEX 20; CON 12; INT 16; WIS 16; CHA 11
Ranger (trapper, wild stalker) 1
Gunslinger (musket master) 5

Feats: Point blank shot, Precise shot, Deadly aim, Rapid shot, Endurance

That's the basic build.
From there my idea is 10 levels of horizon walker focused in mountain, underground and urban terrains.

Thing is I have no idea on what feats to pick from this point.
Also a question: how does terrain mastery work out of combat? Can you always keep the terrain bonus for allies?

Any help will be more than welcome.

[Unien]

No one? :(

[Casual Viking]

You could go Half-Orc and get Endurance from being a Shaman's Apprentice, so you get the Darkvision and other goodies.

Wild stalker gives you +1 Perception. Taking Warden instead gives you your first favored terrain from level 1.