That lighting seems extremely low, in a tank of that depth. I think you could easily go with at least 100 watts of light on that tank and still have a low light tank. Remember that the deeper the tank, the less light reaches the bottom; so any plants that are short will be getting virtually no light when you factor in both the depth and the shading from plants overhead. Java fern and anubias may grow ok, I'm not sure about anything else.

I had a 32g with 40 watts of light for a while, but the tank was only 16" deep. My plants grew very spindly and many plants would just die off. Eventually I grew frustrated and changed my lighting to 60 watts. It's definitely still low light, but the growth is a lot nicer.

If you're sticking with extremely low light and low light plants, I think co2 would not be worth the hassle and could even cause problems if it fluctuates too much. It's likely that you would need to fertilize.

If you're worried about algae, doing water changes and adding ferts will keep algae in check. If you add co2, make sure that you can keep it stable all the time, use a drop checker to keep a close eye on it.