You should have a high DEX-Bonus because you can rise your damage by adding DEX directly (on Level 5) or by reducing your attack roll to increase your damage roll (double Barrel or 2 weapons Shooting simultaneously or feats)
I'm still Level 4 and I got the feat for -1 on attack rolls, +2 on damage rolls, rising every 4 BAB by -1/+2 on this Level, using a musket and dealing 1d10+4 or next Level 1d10+8 damage by adding the Dex-bonus with gun Training
for a normal sized char that would be 1d12+8, if you use a double-Barrel-weapon u get a second dice, for more damage u should get the feat for faster reload, this should be some damage.
And again, Level 7 you get dead shot, asking your GM he may allows you to make a double Barrel shot with both Barrels as a "single attack" for this, giving you 2 additional dices for every additional attack you could do with your BAB, on Level 7 that would be 4d of your weapon, the bigger the weapon the more damage.
If that's not much damage for a touch-attack if u stay in range, then I need references for the damage you want to deal because compared to the last 3 parties I have played or seen this is above average, even the berserk had more, but not much more.
Now comes something which you haven't exactly asked for, but may be also useful. Gunslinger is a class which got also some stats useful if the party lacks a rogue/ranger, with his need of wisdom and dexterity he can use nearly every skill which is important for both of this classes.
Also Gunslinger doesn't Change much for damage calculation if you use small or normal sized classes if you reach Level 5, because the damage step reduces the damage by 1-2 but the static damage rises by 1 for DEX-Bonus all small races I can remember have, so its one of the best Options for damage with small classes.
Using other feats for stealth or similar things, it's nothing special to get a +15 bonus on stealth if you think he should be a bit sneaky to get into a good shooting position (maybe the roof of a near building), if it is a small race, and even normal sized can get a +10 bonus or something close to that very early.
Additionally if you've just got an average chain skirt made of mithril you easily achieve an AC of 20 or even more on low levels without slowing you down in any way (my Kobold Level 4 got 24), which is huge compared to most characters in not-heavy-armor.
It's very important because a gunslinger is a ranged fighter, but he still stays at close range to get the best use with his weapon, so he sometimes gets caught in melee fights.
Better watch the whole pack instead of a single part.
The gunslinger is one of the few classes which get a really decent damage even with a terrible strength, beside magic users, crossbow users and the first hit of a stealthy thief.
Who uses a crossbow as main weapon? No one, it has no style.
And thieves get only a first hit with this damage (maybe with some feats a second one, I'm not sure) IF he is able to sneak.
So only magic users are left and they've got very limited uses of spells.