Crossbow's plenty versatile. You'll rarely go wrong with a small investment in Melee for Dirty Kick (and maybe Expose Weakness, but only if you've got the skill points and feat slot just laying around looking for a home). With that much stealth, you might also want to consider Ambush.
I think your chemistry might be a tiny bit high for that level. If you bring it down to 50, then with your housing bonus you'll still be able to make MKIV grenades and mines. And you won't get much (if any - I think you won't get any but I wouldn't bet the farm on that) Corrosive Acid by level 20. And with that much Dex, if you're willing to carry around the Jackknife for when you need it (it's super light) you can pull 10 points out of lockpicking, too. Then you'd just need 5 more points to get Dirty Kick, if you wanted it; I'd say take it from Stealth but YMMV.
Alternately, if you don't feel like a melee ability is all that desirable for you, you've got the stats for Grenadier, which is a freakishly potent ability. All you'd need is 30 total points in Throwing for it.