For starters, I would HIGHLY recommend reading the water chem primer in the sticky here. One of the major reasons I joined this forum was because there were rational voices of water chemistry, particularly AJ. I actually agree with him, and I tend not to agree with lots of water advice.
I would worry less about the chloride:sulfate ratio, and more about the total sulfate. The more sulfate, the more of a sharp hop bite you'll get. Chloride will not balance that forever. The target ranges you see are more "you probably won't have to dump your beer if you keep them reasonably within this range". And you're fine lower than those. Start low, taste your BEER, then experiment with more salts.
I'll just tell you what I would do, and explain why:
To make my life easier I just mix up 10 gallons of water. I would use 9 gallons RO/Distilled, and 1 gallon tap water. That will start you at 10% original levels:
Ca - 10
Mg - 2
Cl - 0
SO4 - 3
Na - 2
Bicarbonate - 34
Trace elements - very low but present
For most styles I'd add 6 grams CaCl to the water to bump Ca to ~50 and Cl to ~65.
Once you're sure you actually like the sulfate bite to hops, you can try adding some CaSO4 as well. Say 4 grams CaCl and 2 grams CaSO4.
I wouldn't worry too much about darker beers and low pH either... but do test it. You'll likely need some acid for lighter beers and 'maybe' some acid in darker. In my opinion, the spreadsheets and calculators go the crap for dark beers. Don't fear soft water. Look at Alaskan Smoked Porter. I don't know what they do to their water, but it's "glacier fed". I personally believe I like it so much because they leave it softer than most brewers would.