To help out a bit with your questions. Once you become familiar with Rotabutterfly you will probably wonder how you ever got by without it.
To begin, you mentioned re-minerilizing your RO water. Do you use something to contain the RO water before adding it to your aquarium? (I do, 55g plastic drum). If so, follow along;
In Rotalabutterfly the first thing you are asked to do is input your aquarium size (or size of your RO water container). Lets use 55 gallons.
Then answer if DIY or pre-mixed. (Generally I do DIY. But if you are using something that is pre-mixed like Equalibrium then you would answer pre-mixed)
After answering DIY, you are asked to select your compound.
Calcium (Ca) powder from the various suppliers is CaSo4.2H2O.
Magnesium (Mg) crystals from the various suppliers is MgSo4.7H2O.
Sodium Bicarbonate (Baking Soda) is NaHCO3 (I have used this in the past, but the plants don't / can't really use the NaH)(The CO3 is what raises your dKH)
Potassium Bicarbonate (Amazon) is K2CO3 (I am now using this as the plants can use the potassium)(The CO3 is what raises your dKH)
Each of the above can be selected (as a compound) in Rotalabutterfly individually. Lets try MgSO4.7H2O. Then select Dry Dosing as you will be adding the crystals to your RO container.
Now you are asked "I am Calculating For:" - Select "Dose to reach a target". I selected 10ppm. Aiming for a 2:1 ratio of Ca:Mg
Now hit the calculate button.
On the right side of the screen it will tell you how many grams automatic watches
or units of measure to add to your RO container / aquarium to reach your target.
As you can see, it also lists the Mg, S, and dGH amounts. I typically use a spreadsheet to calculate how the individual amounts add up. For example, you should have been given a dGH of 2.31. If I change my compound to CaSo4.2H2O and set my target to 20ppm I will get a dGH of 2.8. So, adding these 2 compounds to your RO water will increase your dGH by 5.11.
Hope the above helps.