Your are starting to overthink things.
Before you add co2 to your water it has a given KH and pH. It also has a general level of CO2. Your base numbers for all three can be measure almost as soon as the tank goes into the water. You do need to roils the surface for a while to insure he dissolved atmospheric gasses are at the natural equilibrium values. So, if you take a small clean container, fill it with your tap water you can test if for a lot of things- chlorine, ammonia, nitrite, nitrate, dissolved co2, oxygen and a few more if you have to. However, even measuring all of this, a lot of things that are in your water are being left out. But the results from this stage are you base yap water levels. So far eazy peazy.
Now you start to add things to the tank, subtrate, decor and perhaps live plants. Some decor and substrate can add things to the water and others can alter the parameters.Curshed coral is an example. The first living thing we all look to have in our tanks are the bacteria which process ammonia trought to nitrate. These guys will use oxygen and carbonates (what makes KH as a supply of inorganic carbon). The there aree live plants which will use CO2 as well. And those live plants also change the amount of nitrifying bacteria one needs since plants can uptake ammonia (as ammonium) way faster than the bacteria can take up the ammonia.
If one does things right, the atmospheric gasses in the water will take care of themselves as long as there is sufficient surface agitation. Most people who keep plants do not need nor do they do anything re co2. It is only when one moves into the range of high light/high tech plants that added Co2 becomes a necessity. The reason is simple, the plants can use up the co2 in the water faster than it can be replaced by surface agitation.
I have had anywhere from my current six planted tanks to as many as a dozen over time and one used pressurized CO2 for a decade. I gave that one up and then slowly decreased the number of planted tanks I have because I am, first and foremost, a fish keeper. The plants were taking too much time which was taken from the fish. Today I do pretty much easy lower light plants and. as I always have, I supplement Flourish Excel after a weekly water change for a carbon boost for the plants. It is worth about 1/3 of adding the gas and a whole lot easier.
If you can, head on over the the YouTube site of an ex-mod here. Rachel, aka msjinkzd, runs a whole lot of planted tanks which look great and to which she adds no ferts and no form of co2.
https://www.youtube.com/user/msjinkzd
Also, I wonder if your tap is 6.5 pH. This is somewhat low for the average municipal supply.
One last note. When I first got into the hobby about 20 years ago, live plants were not so common in tanks. This has changed, a lot. It took me a while to understand there are basically two types of plant keeps in the aquarium hobby. One uses plants for the way they benefit the fish. this includes their abilities to filter the water. Plants can also break up lines of sight, provide hiding places for fry and make a tank look nice. The second type of plant keeper os a plant devotee. The use some of the ,ore "sophisticated" plants and methodologies. They make the p[lants the most important part of a tank and the aquascape a work of art. the fish are secondary. I fall firmly into the first group.
My favorite plant substrate is mulm. I wil;l mot pay extra for soil such as the amazonia and I am not a fan of Amano tanks. I recognize their beauty, but they are not my idea of how to keep fish. I also know that the way to get into planted tanks and to get good at them is the same way one gets good at anything. It takes tme to learn and to gain experience as a primary requirement. One starts simple and works their way up the planted tank learning curve. Trying to do a CO2 added tank as one's first planted tank will almost guarantee failure. It is much like trying to learn to drive in an Indy 600 race car.
This may help you understand some of this all a bit better. Go here:
http://fins.actwin.com/aquariafaq.html then click on
Your First Aquarium then read
Practical Freshwater Chemistry (you can click this but it will not make it easy to peruse the rest of the site).