Mike in RH-
If you are working with 100% RO, then I would have a base Salt addition of:
2g CaSO4
3g MgSO4
5g CaCl2
I would make these same additions to the mash and the sparge.
With 4 gallons of MASH water, that will give you a mash pH at the top end of the range (5.57) and your basic light colored ale. Add 1ml of 88% lactic acid and you're at 5.5 pH.
With 4 gallons of sparge water, your final mineral profile will be:
Calcium Magnesium Sodium Chloride Sulfate Chloride / Sulfate
(Ca ppm) (Mg ppm) (Na ppm) (Cl ppm) (SO4 ppm) Ratio
120 18 0 159 151 1.06
For a hoppy beer, I would reverse the additions of CaSO4 and CaCl2:
5g CaSO4
3g MgSO4
2g CaCl2
Calcium Magnesium Sodium Chloride Sulfate Chloride / Sulfate
(Ca ppm) (Mg ppm) (Na ppm) (Cl ppm) (SO4 ppm) Ratio
111 18 0 64 262 0.24
That would give you a 4:1 Sulfate to Chloride ratio which should be nice and hoppy. My Pliny clone I did with a ratio of 6:1 and it is awesome!!!! You can go as high as 9:1. It will make a HUGE difference in your hop forward beers. If you are going to use your tap water then get the EZ water spreadsheet, and put in your numbers from Ward labs.
PS: 1 teaspoon is about 5 grams of any of these salts.
Dry hopping doesn't add bitterness, but it DOES add flavors. The oils that dissolve into the beer from dry hops will create flavors as well as aromas. Once you get your water profile worked out, I recommend that you give dry hopping another try.