How much light do you have over your aquarium? Light is a main driving factor into whether or not CO2 and fertilizers become a necessity in your aquarium.
The more light you have, the more important the balance between all three becomes.
Since you have CO2, there is no need to be adding Excel at the same time; in fact, CO2 is much better than Excel.
As for fertilizers, as you already know, plants require macronutrients and micronutrients. Of these macronutrients, NPK are the ones that are dosed, while a trace mix is used to dose micronutrients.
For fertilizers, you could always go with commercial products if you want, but they can become very expensive in the long run. Instead, I would recommend you get dry fertilizers instead, and dose from there. That is by far, the cheapest option available to you.
For more information regarding fertilizers and such, please take a look at my primer for planted aquariums linked in my signature below.