Is there any relationship between the levels of KH and GH and the amount of Co2 that will dissolve and be available to my plants?
Nope. Not in our context.
We add CO2 gas.
Whether we add 3 bubbles a second to a 400 liter tank that's got a KH of 1 or a KH 10, we have the Exact same dissolved PPM's of CO2 in both tanks.
CO2 is what plants need, not pH, not a KH(except low KH in a few rare cases, same for fish).
GH is Ca++ and Mg++.
Those are nutrients for plants and can be quite high without issue.
The pH of the water is 7.5. I use pressurized Co2, and a diffuser that is connected to my External filter in the tank.
Then add about 30ppm during the day light cycle and turn it off at night.
Make sure you have good current, some light rippling on the surface, not enough to break the surface.
FYI, my old tank tap water was a KH of 11 and a GH of 24.
Here's what those looked like from Oct 2000:
No RO there.
Plain old EI + good CO2
When you acclimate your fish, take the time to do it right, use an air line dripper and do it slowly. Feed the fish well and make sure they are well taken care of.
There are maybe 10-20 species out 300-400 species of plants that seem to really like softer KH's(3-5 or less), I've not found any plant that hates higher GH's.