Seachem flourish is only a micro nutrient fertiliser. It only supplies micro elements, trace elements and other nutrients. These include calcium, magnesium, iron and other important elements. As you are starting out with plants, it's not going to be the fertiliser that will be lacking. Macro nutrients like Nitrogen (N), Potassium (P) and Phosphorus (K) is what your aquatic plants will need most. Seachem Excel or Glutaraldehyde (or Glut for short) is your alternative to CO2. Once you supply CO2 or Glut, your plants will grow quicker along with high light, this is when the plants will draw up whatever NPK is in your tank and soon exhaust it's supply if you don't supplement it with additional fertiliser. Personally, I would just add your plants without these ferts yet. Observe the plants growth and then introduce ferts if necessary. Nitrogen (N) and Phosphorus(K) will occur naturally in your tank - Shrimp waste, food, etc are sources of such things. Only Potassium (P) will be lacking. Watch for Macro nutrient deficiencies then add as necessary. Not adding ferts might mean that plants won't grow as fast. But then the plus is that you have less trimming and plant maintenance. On another personal note, I won't add Excel or Glut into my shrimp tanks. Fish tank yes, but not delicate shrimps. Glut is from the Aldehyde after all - it's a disinfectant, and it's the stuff they use in jars to preserve specimens. You know, the stuff you see in museums held in jars with liquid. Some people have used glut or excel with no effects, but I don't want to risk it. Flourish and micro nutrients aren't as essential until you sort out NPK. But again, I would try the plants out without ferts yet. Watch for plants exhibiting micro nutrient deficiencies then add as necessary. My shrimp tank is heavily planted relative to the size of the tank, and plants are all doing well. I don't add any fertiliser apart from Calcium, magnesium, and shrimp food. Get the balance with lighting correct and you will find ferts are not going to be the critical ingredient.