Not all 3 are going to happen.
Ideally Spike would probably be closer to
Str 12 (slightly above average, his fighting style is more Dex based)
Dex 20+ (as high as possible, AC/dodging, Ranged weapons, etc...)
Con 18 (dude can take a serious beating)
Int 10 (much more "street smart" than "book smart")
Wis 16 (then again, I think a 16 is still pushing it...)
Cha 12 (he thinks he's all that and a bag of chips, but...)
I guess a more realistic "budget" Spike would be closer to
Dex 16 (18 after racials, can't afford to go higher)
Con 12 (still a boost, but less so)
Int 8 (with the Human Skill bonus he breaks even Skill-wise)
What about the Feats?
The problem is that there is a sizable bottle-neck right around level 8-to-10.
It's when Deft Shootist comes online, the ideal point to take Improved Critical, and the absolute earliest we can get Snap Shot online.
I feel Deft Shootist has priority, but is there something else I can move around?
Snap Shot is also being quite the pain with, essentially, FOUR required feats (Point-Blank, Rapid Shot, Weapon Focus, and Combat Reflexes).
I'm thinking I'm going to have to add 2 levels of Fighter just after Gunslinger 5 just for the feats (Mobile Fighter and Tactician are the current front-runners).