Even if you could get Wis-To-Hit, you'd still want a decent Dex score to qualify for feats.
Although, if you can get your DM to rule that Zen Archer Monk can use Wis-To-Hit with Firearms, then you could get away with as low as 13 Dex, taking all the High Dex Req feats with the Monk's Bonus feats.
Also, Cieyrin, you may want to mention (probably in the Stats section) that a Gunslinger with 7 (or less) Wis still has the same size Grit pool as a 'Slinger with 13 Wis.
And that a 'Slinger with low Wis and the Extra Grit Feat has as much Grit as a 'Slinger with 16 Dex. So a Low(er)-Wis build is an option.