What I am going to do is supply you with a link.
Understanding Water Conditioners
I think this might be enough to get you started. A water softener is not a "toaster". You did the firsy step in getting your water analyzed and you don't have to worry about iron.
What you also have to think about as to what water you want to have softened. Outdoor taps usually are not. You might not want to do a laundry sink either.
Softening costs money, so generally you don't soften everything.
Your family size, water usage, space available will pay a role somewhat. So will capacity as in the ability to neutralize. Your gram figure is proabably grains of hardness. 20 grams is a lot. That's like the weight of 20 ml of water.
20 grams is the weight of about 1.4 tablespoons of water.
20 grains is about the weight of 0.26 TEASPONS
Big difference.
I used onlineconversion.com, and used a relationship that 1 CC (Cubic centimeter) = 1 ml (millileter) = 1 gram of pure water. This is true because water has a density of 1gram/CC.
Since your on well water, you probably don't know how much water you use.
See what you come up with.
You can estimate requirements, by filling buckets. SHower, dishes. Clothes might be harder, but not really. Collect the amont of water at each level.
Outdoor watering will be the toughest.
You might be able to get an idea of the max flow and the usage rates by estimating with a few bucket fills and a stop watch.