Are the 2x 20W lights meant to be for plants or to view the tank? I would change out those bulbs.
Anyway, to answer your question, the basic gist of plant growth works like this:
Light drives all growth. With more light comes the need for more CO2. With more CO2 comes the need for macro nutrients, or NPK (Nitrogen, Phosphate, Potassium). Some of these, mainly nitrogen and phosphate, can come from fish waste and fish food. However, if you have high enough light and you are giving the plants sufficient CO2, you will probably need to add NPK (emphasis on the Potassium, K). Think of these as plant food. Plants also require micronutrients, or trace fertilizer. These include iron, which you are already dosing, magnesium, calcium, and other things that I can't remember. Think of these as plant vitamins. You probably don't need to dose Fe alone. You could get away with dosing just a trace fertilizer, such as CSM+B, a dry fertilizer, or Flourish (regular Flourish). Be careful when dosing these not to overdose much, as they contain copper, which invertebrates are very sensitive to.
Your current amount of light is just on the cusp of low tech and high tech, so I guess you could call it mid tech. Since you are using DIY CO2, I recommend you keep up with it, as unstable CO2 could cause algae problems later. Use a bubble counter and a check valve to monitor the CO2 production in your bottle and to prevent siphon action. Keep up with your yeast mixtures, and change them out when you start to see the bubble count slow down. I would also recommend you consider running more than one bottle, starting them on staggered weeks. Also, you may want to start a bottle before the first one stops producing. Finally, since you are using a Penguin, I would recommend you remove the biowheel and keep the tank topped off to reduce surface agitation.
A popular method with many people on this forum is the EI method. EI, or estimated index, is designed to reduce the need for testing. This is good because many tests are completely inaccurate and useless (for example, iron. It is unlikely you had absolutely no iron in your water). The basic idea with EI is to ensure plants have enough of all nutrients, then dilute them at the end of the week with a large water change. This ensures that there isn't a ton of excess nutrients for algae to use.
Here are some places to start looking for dosing info: