Blackwood,
The API Freshwater master kit is a great test kit, and it is reasonably priced. It uses liquid titration tests, which are far more accurate and reliable than the test strips.
When you say you have no buffers, I am not sure what you mean -- your KH is in a good range, should be fine.
What kind of CO2 system are you going to get? DIY or pressurized?
As far as how many bubbles per second you should aim for it depends on how you are dosing your CO2. For example if you use an electric selenoid on a timer, and run it for 8 hours a day, you may need more than if you run it for 12 hours a day, etc. You can also set up an electric selenoid with a pH controller that will keep your CO2 concentration almost constant, at which point bubbles per second is not all that important, so long as it is in the 1-5 or so bubbles per second range (because the pH controller will turn the Co2 off and on based on pH readings).
pH is important because when combined with KH measurements, you can determine your CO2 ppm (although accuracy varies based on the type/amount of buffers that are in your water).
To do this, you use the following formula:
CO2 (in PPM) = 3 * KH * 10^(7-pH)
(where kH is in degrees, not ppm as you posted. You can convert from ppm to degrees by dividing ppm by 17.9)
"Bubble checkers": I believe you are referring to drop checkers. Yes, they are a great tool. They operate on the same principle I described above, so long as you use a constant KH reference solution in the checker (NOT tap water or aquarium water, as many of the directions that come with the checker say to do). If you use a 4 degrees Carbonic Hardness (KH) solution, you know the KH reading, so that is constant. We know that CO2 alters pH, so if we have a constant KH, and use a pH indicating solution (bromothymol blue) in the drop checker, the solution inside will change colors based on the amount of CO2 that is dissolved into the water. The most common reference solution is 4dKH because that indicates a nice dark green color right around the sweet spot of 30-40 ppm CO2 or so. Get much below that and the pH raises, and the indicating solution turns blue. Get much above that range (say 50+ppm) and the solution turns a yellow-green color. They are a very handy tool to allow you at a glance to see almost in real time (the checker takes some time to reach equilibrium with the water, around a 1/2 hour or so delay) what your Co2 is reading. And yes, it stays in your tank all the time. The bromothymol blue fades over time -- I change the solution in my drop checkers about every 3-4 weeks.
On to ferts: At less than 2 watts per gallon, you will probably not need a very high tech / high intensity fertilizing regiment. Depending on bioload in your tank, you may benefit from adding some N. A trace mix that includes Fe and another mix with K (potassium) may be beneficial. Your tank may or may not be P limited. I would suggest starting with a trace mix and some K, and see where that takes you. Your API freshwater kit (or your test strips for that matter) will let you know if you are bottoming out at all on N (NitrAtes). You want your Nitrates to stay around 10-20ppm in a planted tank. If you have fast growers, even in your medium low to low light tank, you might have to dose some N.
You can also pick up Fe and P (phosphorus) test kits to check those levels in your tank to give you some extra peace of mind, but they are not required. The kits are 10-20$ each. Rather than test for Fe or P, you can just check for symptoms of nutrient deficiencies in your plants (click the plant resources link in my signature, there are some good tables there that will show symptoms of nutrient deficiency) and modify your fert regiment based on what you see. I personally am a numbers kind of guy, so I go the test route (although pretty infrequently -- I watch my plants, dose here and there, and test to verify about every 3-4 weeks). It does not have to be an exact science. The key is not to become limited by any of your macros (N, P, and K) and provide enough trace to keep deficiencies at bay.
Anyway, that should give you enough to read for awhile. Best of luck!
