Whether you need co2 really depends on whether you have high light and how much you intend to fertilize. That in turn determines what kind of plants you can grow successfully. As long as you're set up with a low-medium light and don't intend to fertilize frequently, if at all, then you'll be fine with growing low-med light plants and no co2.
Looks like a nice home for your CDPs.
I have both low light and high light plants in my nano tank. I haven't use any plant fertilize in my tank and my lighting is not bright, but Sunset Hygrophila retained it's nice color LOL.
I saw your nano tank, it is very pretty
Let me know its recent development.