The anubias and java moss are grown attached to decor and moss balls sit on top of the substrate, so root tabs are no use, you'll need a liquid fertiliser. Not all liquid fertilisers contain all the micronutrients needed by plants, the best ones are Seachem Flourish comprehensive supplement and Brightwell FlorinMulti. Make sure you buy one of those two with exactly those names as both companies make other similarly named products.
If you intend to get more plants which are rooted in the substrate and you don't have a fertiliser enriched substrate you will need root tabs for them - Seachem root tabs come highly recommended as they don't pollute the water like some other brands.
With slow growing plants like yours there is no benefit in using CO2. Even with fast growing plants if you intend to have fish in the tank, CO2 is not advised as it can harm fish. Thefish will produce enough CO2, as will the bacteria in the substrate as they break down waste matter to form carbon dioxide.
As for when to start adding the fertiliser, I would add it now.