I was doing the same research yesterday. BTW; don't envy the 10g,
it has sprung a leak. I'm going to tap that free 10g source and see if
I can get the leaky one drained & planted today.
With regard to the ph/Gh/KH relationships; the high ph (that I have) is not as
big an issue as maintaining stable ph. Keeping in mind that the difference between
7 & 7.1 is a tenfold increase. Same for K & G, they are all logarithmic.
Since my math skillset does not include advanced math, I comprehend
the concept but not the working problems.
According to research, it would also be my method to finish the cycling, then attempt to correct KH & GH. I have noticed the following; as the water in the tanks ages, (evaporates & concentrates salts) my ph rises from 7.8 to 8, my GH rises about 3 levels and my KH decreases a level or two over approximately 5 days.
Again according to research, KH of anywhere from 80 to 150 is generally good.
Quoting from a site I cannot link to;
"GH is an area of aquarium chemistry where there is a lot of misunderstanding or simply down right wrong advice. I have received many a call, email, etc. over the years what do about their so-called high GH, often this GH turns out to be around 200 ppm which is fine for most fish (low for African Cichlids, and even livebearers and goldfish do better at higher GH). This is based on old assumptions of respiration in fish, as well as lack of understanding of the importance of positive Calcium ions (as well as Magnesium & Potassium) in the regulation of MANY bio processes in fish including healing, heart function, and regulation of osmotic functions."
"Although many aquarists worry about “too high GH” (based on respiration problems), this is based on long proven false myths. In reality freshwater generally it would take a GH of over 500 ppm to cause this problem."
So I conclude that my GH at highest reading of 12/214.8ppm & KH at lowest reading of 6/89.4 are well within acceptable ranges despite the high ph which is stable.
Keep us posted!
P.S. With regard to water changes; I did one 90% change in both tanks during cycling. Additionally, used the water for the 90% change in the 5g. When my chems reached 0/0/<6ppm, I acclimated the fish both times. I used the two hour drip method. Here is a link to the process in the 10g: Drip Acclimation for Freshwater fish.
Keep the driftwood if you already have it, or want it for aqua-scaping. It will affect the ph a little but
with your reading, it will not hurt anything. Your ph should stabilize again at a lower reading relative
to the tannins released by the wood. Make sure you soak it for a week or two before introducing
it into the tank if it floats or you are unsure where it was harvested.